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linux/arch/arm64/kernel/signal.c
Marco Elver 60768ffced signal: Deliver SIGTRAP on perf event asynchronously if blocked 
[ Upstream commit 78ed93d72d ]

With SIGTRAP on perf events, we have encountered termination of
processes due to user space attempting to block delivery of SIGTRAP.
Consider this case:

    <set up SIGTRAP on a perf event>
    ...
    sigset_t s;
    sigemptyset(&s);
    sigaddset(&s, SIGTRAP | <and others>);
    sigprocmask(SIG_BLOCK, &s, ...);
    ...
    <perf event triggers>

When the perf event triggers, while SIGTRAP is blocked, force_sig_perf()
will force the signal, but revert back to the default handler, thus
terminating the task.

This makes sense for error conditions, but not so much for explicitly
requested monitoring. However, the expectation is still that signals
generated by perf events are synchronous, which will no longer be the
case if the signal is blocked and delivered later.

To give user space the ability to clearly distinguish synchronous from
asynchronous signals, introduce siginfo_t::si_perf_flags and
TRAP_PERF_FLAG_ASYNC (opted for flags in case more binary information is
required in future).

The resolution to the problem is then to (a) no longer force the signal
(avoiding the terminations), but (b) tell user space via si_perf_flags
if the signal was synchronous or not, so that such signals can be
handled differently (e.g. let user space decide to ignore or consider
the data imprecise).

The alternative of making the kernel ignore SIGTRAP on perf events if
the signal is blocked may work for some usecases, but likely causes
issues in others that then have to revert back to interception of
sigprocmask() (which we want to avoid). [ A concrete example: when using
breakpoint perf events to track data-flow, in a region of code where
signals are blocked, data-flow can no longer be tracked accurately.
When a relevant asynchronous signal is received after unblocking the
signal, the data-flow tracking logic needs to know its state is
imprecise. ]

Fixes: 97ba62b278 ("perf: Add support for SIGTRAP on perf events")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Link: https://lore.kernel.org/r/20220404111204.935357-1-elver@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-06-09 10:22:48 +02:00

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Based on arch/arm/kernel/signal.c
*
* Copyright (C) 1995-2009 Russell King
* Copyright (C) 2012 ARM Ltd.
*/
#include <linux/cache.h>
#include <linux/compat.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/freezer.h>
#include <linux/stddef.h>
#include <linux/uaccess.h>
#include <linux/sizes.h>
#include <linux/string.h>
#include <linux/tracehook.h>
#include <linux/ratelimit.h>
#include <linux/syscalls.h>
#include <asm/daifflags.h>
#include <asm/debug-monitors.h>
#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/fpsimd.h>
#include <asm/ptrace.h>
#include <asm/syscall.h>
#include <asm/signal32.h>
#include <asm/traps.h>
#include <asm/vdso.h>
/*
* Do a signal return; undo the signal stack. These are aligned to 128-bit.
*/
struct rt_sigframe {
struct siginfo info;
struct ucontext uc;
};
struct frame_record {
u64 fp;
u64 lr;
};
struct rt_sigframe_user_layout {
struct rt_sigframe __user *sigframe;
struct frame_record __user *next_frame;
unsigned long size; /* size of allocated sigframe data */
unsigned long limit; /* largest allowed size */
unsigned long fpsimd_offset;
unsigned long esr_offset;
unsigned long sve_offset;
unsigned long extra_offset;
unsigned long end_offset;
};
#define BASE_SIGFRAME_SIZE round_up(sizeof(struct rt_sigframe), 16)
#define TERMINATOR_SIZE round_up(sizeof(struct _aarch64_ctx), 16)
#define EXTRA_CONTEXT_SIZE round_up(sizeof(struct extra_context), 16)
static void init_user_layout(struct rt_sigframe_user_layout *user)
{
const size_t reserved_size =
sizeof(user->sigframe->uc.uc_mcontext.__reserved);
memset(user, 0, sizeof(*user));
user->size = offsetof(struct rt_sigframe, uc.uc_mcontext.__reserved);
user->limit = user->size + reserved_size;
user->limit -= TERMINATOR_SIZE;
user->limit -= EXTRA_CONTEXT_SIZE;
/* Reserve space for extension and terminator ^ */
}
static size_t sigframe_size(struct rt_sigframe_user_layout const *user)
{
return round_up(max(user->size, sizeof(struct rt_sigframe)), 16);
}
/*
* Sanity limit on the approximate maximum size of signal frame we'll
* try to generate. Stack alignment padding and the frame record are
* not taken into account. This limit is not a guarantee and is
* NOT ABI.
*/
#define SIGFRAME_MAXSZ SZ_64K
static int __sigframe_alloc(struct rt_sigframe_user_layout *user,
unsigned long *offset, size_t size, bool extend)
{
size_t padded_size = round_up(size, 16);
if (padded_size > user->limit - user->size &&
!user->extra_offset &&
extend) {
int ret;
user->limit += EXTRA_CONTEXT_SIZE;
ret = __sigframe_alloc(user, &user->extra_offset,
sizeof(struct extra_context), false);
if (ret) {
user->limit -= EXTRA_CONTEXT_SIZE;
return ret;
}
/* Reserve space for the __reserved[] terminator */
user->size += TERMINATOR_SIZE;
/*
* Allow expansion up to SIGFRAME_MAXSZ, ensuring space for
* the terminator:
*/
user->limit = SIGFRAME_MAXSZ - TERMINATOR_SIZE;
}
/* Still not enough space? Bad luck! */
if (padded_size > user->limit - user->size)
return -ENOMEM;
*offset = user->size;
user->size += padded_size;
return 0;
}
/*
* Allocate space for an optional record of <size> bytes in the user
* signal frame. The offset from the signal frame base address to the
* allocated block is assigned to *offset.
*/
static int sigframe_alloc(struct rt_sigframe_user_layout *user,
unsigned long *offset, size_t size)
{
return __sigframe_alloc(user, offset, size, true);
}
/* Allocate the null terminator record and prevent further allocations */
static int sigframe_alloc_end(struct rt_sigframe_user_layout *user)
{
int ret;
/* Un-reserve the space reserved for the terminator: */
user->limit += TERMINATOR_SIZE;
ret = sigframe_alloc(user, &user->end_offset,
sizeof(struct _aarch64_ctx));
if (ret)
return ret;
/* Prevent further allocation: */
user->limit = user->size;
return 0;
}
static void __user *apply_user_offset(
struct rt_sigframe_user_layout const *user, unsigned long offset)
{
char __user *base = (char __user *)user->sigframe;
return base + offset;
}
static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
{
struct user_fpsimd_state const *fpsimd =
&current->thread.uw.fpsimd_state;
int err;
/* copy the FP and status/control registers */
err = __copy_to_user(ctx->vregs, fpsimd->vregs, sizeof(fpsimd->vregs));
__put_user_error(fpsimd->fpsr, &ctx->fpsr, err);
__put_user_error(fpsimd->fpcr, &ctx->fpcr, err);
/* copy the magic/size information */
__put_user_error(FPSIMD_MAGIC, &ctx->head.magic, err);
__put_user_error(sizeof(struct fpsimd_context), &ctx->head.size, err);
return err ? -EFAULT : 0;
}
static int restore_fpsimd_context(struct fpsimd_context __user *ctx)
{
struct user_fpsimd_state fpsimd;
__u32 magic, size;
int err = 0;
/* check the magic/size information */
__get_user_error(magic, &ctx->head.magic, err);
__get_user_error(size, &ctx->head.size, err);
if (err)
return -EFAULT;
if (magic != FPSIMD_MAGIC || size != sizeof(struct fpsimd_context))
return -EINVAL;
/* copy the FP and status/control registers */
err = __copy_from_user(fpsimd.vregs, ctx->vregs,
sizeof(fpsimd.vregs));
__get_user_error(fpsimd.fpsr, &ctx->fpsr, err);
__get_user_error(fpsimd.fpcr, &ctx->fpcr, err);
clear_thread_flag(TIF_SVE);
/* load the hardware registers from the fpsimd_state structure */
if (!err)
fpsimd_update_current_state(&fpsimd);
return err ? -EFAULT : 0;
}
struct user_ctxs {
struct fpsimd_context __user *fpsimd;
struct sve_context __user *sve;
};
#ifdef CONFIG_ARM64_SVE
static int preserve_sve_context(struct sve_context __user *ctx)
{
int err = 0;
u16 reserved[ARRAY_SIZE(ctx->__reserved)];
unsigned int vl = current->thread.sve_vl;
unsigned int vq = 0;
if (test_thread_flag(TIF_SVE))
vq = sve_vq_from_vl(vl);
memset(reserved, 0, sizeof(reserved));
__put_user_error(SVE_MAGIC, &ctx->head.magic, err);
__put_user_error(round_up(SVE_SIG_CONTEXT_SIZE(vq), 16),
&ctx->head.size, err);
__put_user_error(vl, &ctx->vl, err);
BUILD_BUG_ON(sizeof(ctx->__reserved) != sizeof(reserved));
err |= __copy_to_user(&ctx->__reserved, reserved, sizeof(reserved));
if (vq) {
/*
* This assumes that the SVE state has already been saved to
* the task struct by calling the function
* fpsimd_signal_preserve_current_state().
*/
err |= __copy_to_user((char __user *)ctx + SVE_SIG_REGS_OFFSET,
current->thread.sve_state,
SVE_SIG_REGS_SIZE(vq));
}
return err ? -EFAULT : 0;
}
static int restore_sve_fpsimd_context(struct user_ctxs *user)
{
int err;
unsigned int vq;
struct user_fpsimd_state fpsimd;
struct sve_context sve;
if (__copy_from_user(&sve, user->sve, sizeof(sve)))
return -EFAULT;
if (sve.vl != current->thread.sve_vl)
return -EINVAL;
if (sve.head.size <= sizeof(*user->sve)) {
clear_thread_flag(TIF_SVE);
goto fpsimd_only;
}
vq = sve_vq_from_vl(sve.vl);
if (sve.head.size < SVE_SIG_CONTEXT_SIZE(vq))
return -EINVAL;
/*
* Careful: we are about __copy_from_user() directly into
* thread.sve_state with preemption enabled, so protection is
* needed to prevent a racing context switch from writing stale
* registers back over the new data.
*/
fpsimd_flush_task_state(current);
/* From now, fpsimd_thread_switch() won't touch thread.sve_state */
sve_alloc(current);
if (!current->thread.sve_state) {
clear_thread_flag(TIF_SVE);
return -ENOMEM;
}
err = __copy_from_user(current->thread.sve_state,
(char __user const *)user->sve +
SVE_SIG_REGS_OFFSET,
SVE_SIG_REGS_SIZE(vq));
if (err)
return -EFAULT;
set_thread_flag(TIF_SVE);
fpsimd_only:
/* copy the FP and status/control registers */
/* restore_sigframe() already checked that user->fpsimd != NULL. */
err = __copy_from_user(fpsimd.vregs, user->fpsimd->vregs,
sizeof(fpsimd.vregs));
__get_user_error(fpsimd.fpsr, &user->fpsimd->fpsr, err);
__get_user_error(fpsimd.fpcr, &user->fpsimd->fpcr, err);
/* load the hardware registers from the fpsimd_state structure */
if (!err)
fpsimd_update_current_state(&fpsimd);
return err ? -EFAULT : 0;
}
#else /* ! CONFIG_ARM64_SVE */
/* Turn any non-optimised out attempts to use these into a link error: */
extern int preserve_sve_context(void __user *ctx);
extern int restore_sve_fpsimd_context(struct user_ctxs *user);
#endif /* ! CONFIG_ARM64_SVE */
static int parse_user_sigframe(struct user_ctxs *user,
struct rt_sigframe __user *sf)
{
struct sigcontext __user *const sc = &sf->uc.uc_mcontext;
struct _aarch64_ctx __user *head;
char __user *base = (char __user *)&sc->__reserved;
size_t offset = 0;
size_t limit = sizeof(sc->__reserved);
bool have_extra_context = false;
char const __user *const sfp = (char const __user *)sf;
user->fpsimd = NULL;
user->sve = NULL;
if (!IS_ALIGNED((unsigned long)base, 16))
goto invalid;
while (1) {
int err = 0;
u32 magic, size;
char const __user *userp;
struct extra_context const __user *extra;
u64 extra_datap;
u32 extra_size;
struct _aarch64_ctx const __user *end;
u32 end_magic, end_size;
if (limit - offset < sizeof(*head))
goto invalid;
if (!IS_ALIGNED(offset, 16))
goto invalid;
head = (struct _aarch64_ctx __user *)(base + offset);
__get_user_error(magic, &head->magic, err);
__get_user_error(size, &head->size, err);
if (err)
return err;
if (limit - offset < size)
goto invalid;
switch (magic) {
case 0:
if (size)
goto invalid;
goto done;
case FPSIMD_MAGIC:
if (!system_supports_fpsimd())
goto invalid;
if (user->fpsimd)
goto invalid;
if (size < sizeof(*user->fpsimd))
goto invalid;
user->fpsimd = (struct fpsimd_context __user *)head;
break;
case ESR_MAGIC:
/* ignore */
break;
case SVE_MAGIC:
if (!system_supports_sve())
goto invalid;
if (user->sve)
goto invalid;
if (size < sizeof(*user->sve))
goto invalid;
user->sve = (struct sve_context __user *)head;
break;
case EXTRA_MAGIC:
if (have_extra_context)
goto invalid;
if (size < sizeof(*extra))
goto invalid;
userp = (char const __user *)head;
extra = (struct extra_context const __user *)userp;
userp += size;
__get_user_error(extra_datap, &extra->datap, err);
__get_user_error(extra_size, &extra->size, err);
if (err)
return err;
/* Check for the dummy terminator in __reserved[]: */
if (limit - offset - size < TERMINATOR_SIZE)
goto invalid;
end = (struct _aarch64_ctx const __user *)userp;
userp += TERMINATOR_SIZE;
__get_user_error(end_magic, &end->magic, err);
__get_user_error(end_size, &end->size, err);
if (err)
return err;
if (end_magic || end_size)
goto invalid;
/* Prevent looping/repeated parsing of extra_context */
have_extra_context = true;
base = (__force void __user *)extra_datap;
if (!IS_ALIGNED((unsigned long)base, 16))
goto invalid;
if (!IS_ALIGNED(extra_size, 16))
goto invalid;
if (base != userp)
goto invalid;
/* Reject "unreasonably large" frames: */
if (extra_size > sfp + SIGFRAME_MAXSZ - userp)
goto invalid;
/*
* Ignore trailing terminator in __reserved[]
* and start parsing extra data:
*/
offset = 0;
limit = extra_size;
if (!access_ok(base, limit))
goto invalid;
continue;
default:
goto invalid;
}
if (size < sizeof(*head))
goto invalid;
if (limit - offset < size)
goto invalid;
offset += size;
}
done:
return 0;
invalid:
return -EINVAL;
}
static int restore_sigframe(struct pt_regs *regs,
struct rt_sigframe __user *sf)
{
sigset_t set;
int i, err;
struct user_ctxs user;
err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
if (err == 0)
set_current_blocked(&set);
for (i = 0; i < 31; i++)
__get_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
err);
__get_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
__get_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
__get_user_error(regs->pstate, &sf->uc.uc_mcontext.pstate, err);
/*
* Avoid sys_rt_sigreturn() restarting.
*/
forget_syscall(regs);
err |= !valid_user_regs(&regs->user_regs, current);
if (err == 0)
err = parse_user_sigframe(&user, sf);
if (err == 0 && system_supports_fpsimd()) {
if (!user.fpsimd)
return -EINVAL;
if (user.sve) {
if (!system_supports_sve())
return -EINVAL;
err = restore_sve_fpsimd_context(&user);
} else {
err = restore_fpsimd_context(user.fpsimd);
}
}
return err;
}
SYSCALL_DEFINE0(rt_sigreturn)
{
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe __user *frame;
/* Always make any pending restarted system calls return -EINTR */
current->restart_block.fn = do_no_restart_syscall;
/*
* Since we stacked the signal on a 128-bit boundary, then 'sp' should
* be word aligned here.
*/
if (regs->sp & 15)
goto badframe;
frame = (struct rt_sigframe __user *)regs->sp;
if (!access_ok(frame, sizeof (*frame)))
goto badframe;
if (restore_sigframe(regs, frame))
goto badframe;
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
return regs->regs[0];
badframe:
arm64_notify_segfault(regs->sp);
return 0;
}
/*
* Determine the layout of optional records in the signal frame
*
* add_all: if true, lays out the biggest possible signal frame for
* this task; otherwise, generates a layout for the current state
* of the task.
*/
static int setup_sigframe_layout(struct rt_sigframe_user_layout *user,
bool add_all)
{
int err;
if (system_supports_fpsimd()) {
err = sigframe_alloc(user, &user->fpsimd_offset,
sizeof(struct fpsimd_context));
if (err)
return err;
}
/* fault information, if valid */
if (add_all || current->thread.fault_code) {
err = sigframe_alloc(user, &user->esr_offset,
sizeof(struct esr_context));
if (err)
return err;
}
if (system_supports_sve()) {
unsigned int vq = 0;
if (add_all || test_thread_flag(TIF_SVE)) {
int vl = sve_max_vl;
if (!add_all)
vl = current->thread.sve_vl;
vq = sve_vq_from_vl(vl);
}
err = sigframe_alloc(user, &user->sve_offset,
SVE_SIG_CONTEXT_SIZE(vq));
if (err)
return err;
}
return sigframe_alloc_end(user);
}
static int setup_sigframe(struct rt_sigframe_user_layout *user,
struct pt_regs *regs, sigset_t *set)
{
int i, err = 0;
struct rt_sigframe __user *sf = user->sigframe;
/* set up the stack frame for unwinding */
__put_user_error(regs->regs[29], &user->next_frame->fp, err);
__put_user_error(regs->regs[30], &user->next_frame->lr, err);
for (i = 0; i < 31; i++)
__put_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
err);
__put_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
__put_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
__put_user_error(regs->pstate, &sf->uc.uc_mcontext.pstate, err);
__put_user_error(current->thread.fault_address, &sf->uc.uc_mcontext.fault_address, err);
err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));
if (err == 0 && system_supports_fpsimd()) {
struct fpsimd_context __user *fpsimd_ctx =
apply_user_offset(user, user->fpsimd_offset);
err |= preserve_fpsimd_context(fpsimd_ctx);
}
/* fault information, if valid */
if (err == 0 && user->esr_offset) {
struct esr_context __user *esr_ctx =
apply_user_offset(user, user->esr_offset);
__put_user_error(ESR_MAGIC, &esr_ctx->head.magic, err);
__put_user_error(sizeof(*esr_ctx), &esr_ctx->head.size, err);
__put_user_error(current->thread.fault_code, &esr_ctx->esr, err);
}
/* Scalable Vector Extension state, if present */
if (system_supports_sve() && err == 0 && user->sve_offset) {
struct sve_context __user *sve_ctx =
apply_user_offset(user, user->sve_offset);
err |= preserve_sve_context(sve_ctx);
}
if (err == 0 && user->extra_offset) {
char __user *sfp = (char __user *)user->sigframe;
char __user *userp =
apply_user_offset(user, user->extra_offset);
struct extra_context __user *extra;
struct _aarch64_ctx __user *end;
u64 extra_datap;
u32 extra_size;
extra = (struct extra_context __user *)userp;
userp += EXTRA_CONTEXT_SIZE;
end = (struct _aarch64_ctx __user *)userp;
userp += TERMINATOR_SIZE;
/*
* extra_datap is just written to the signal frame.
* The value gets cast back to a void __user *
* during sigreturn.
*/
extra_datap = (__force u64)userp;
extra_size = sfp + round_up(user->size, 16) - userp;
__put_user_error(EXTRA_MAGIC, &extra->head.magic, err);
__put_user_error(EXTRA_CONTEXT_SIZE, &extra->head.size, err);
__put_user_error(extra_datap, &extra->datap, err);
__put_user_error(extra_size, &extra->size, err);
/* Add the terminator */
__put_user_error(0, &end->magic, err);
__put_user_error(0, &end->size, err);
}
/* set the "end" magic */
if (err == 0) {
struct _aarch64_ctx __user *end =
apply_user_offset(user, user->end_offset);
__put_user_error(0, &end->magic, err);
__put_user_error(0, &end->size, err);
}
return err;
}
static int get_sigframe(struct rt_sigframe_user_layout *user,
struct ksignal *ksig, struct pt_regs *regs)
{
unsigned long sp, sp_top;
int err;
init_user_layout(user);
err = setup_sigframe_layout(user, false);
if (err)
return err;
sp = sp_top = sigsp(regs->sp, ksig);
sp = round_down(sp - sizeof(struct frame_record), 16);
user->next_frame = (struct frame_record __user *)sp;
sp = round_down(sp, 16) - sigframe_size(user);
user->sigframe = (struct rt_sigframe __user *)sp;
/*
* Check that we can actually write to the signal frame.
*/
if (!access_ok(user->sigframe, sp_top - sp))
return -EFAULT;
return 0;
}
static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
struct rt_sigframe_user_layout *user, int usig)
{
__sigrestore_t sigtramp;
regs->regs[0] = usig;
regs->sp = (unsigned long)user->sigframe;
regs->regs[29] = (unsigned long)&user->next_frame->fp;
regs->pc = (unsigned long)ka->sa.sa_handler;
/*
* Signal delivery is a (wacky) indirect function call in
* userspace, so simulate the same setting of BTYPE as a BLR
* <register containing the signal handler entry point>.
* Signal delivery to a location in a PROT_BTI guarded page
* that is not a function entry point will now trigger a
* SIGILL in userspace.
*
* If the signal handler entry point is not in a PROT_BTI
* guarded page, this is harmless.
*/
if (system_supports_bti()) {
regs->pstate &= ~PSR_BTYPE_MASK;
regs->pstate |= PSR_BTYPE_C;
}
/* TCO (Tag Check Override) always cleared for signal handlers */
regs->pstate &= ~PSR_TCO_BIT;
if (ka->sa.sa_flags & SA_RESTORER)
sigtramp = ka->sa.sa_restorer;
else
sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp);
regs->regs[30] = (unsigned long)sigtramp;
}
static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
struct pt_regs *regs)
{
struct rt_sigframe_user_layout user;
struct rt_sigframe __user *frame;
int err = 0;
fpsimd_signal_preserve_current_state();
if (get_sigframe(&user, ksig, regs))
return 1;
frame = user.sigframe;
__put_user_error(0, &frame->uc.uc_flags, err);
__put_user_error(NULL, &frame->uc.uc_link, err);
err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
err |= setup_sigframe(&user, regs, set);
if (err == 0) {
setup_return(regs, &ksig->ka, &user, usig);
if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
err |= copy_siginfo_to_user(&frame->info, &ksig->info);
regs->regs[1] = (unsigned long)&frame->info;
regs->regs[2] = (unsigned long)&frame->uc;
}
}
return err;
}
static void setup_restart_syscall(struct pt_regs *regs)
{
if (is_compat_task())
compat_setup_restart_syscall(regs);
else
regs->regs[8] = __NR_restart_syscall;
}
/*
* OK, we're invoking a handler
*/
static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
sigset_t *oldset = sigmask_to_save();
int usig = ksig->sig;
int ret;
rseq_signal_deliver(ksig, regs);
/*
* Set up the stack frame
*/
if (is_compat_task()) {
if (ksig->ka.sa.sa_flags & SA_SIGINFO)
ret = compat_setup_rt_frame(usig, ksig, oldset, regs);
else
ret = compat_setup_frame(usig, ksig, oldset, regs);
} else {
ret = setup_rt_frame(usig, ksig, oldset, regs);
}
/*
* Check that the resulting registers are actually sane.
*/
ret |= !valid_user_regs(&regs->user_regs, current);
/* Step into the signal handler if we are stepping */
signal_setup_done(ret, ksig, test_thread_flag(TIF_SINGLESTEP));
}
/*
* Note that 'init' is a special process: it doesn't get signals it doesn't
* want to handle. Thus you cannot kill init even with a SIGKILL even by
* mistake.
*
* Note that we go through the signals twice: once to check the signals that
* the kernel can handle, and then we build all the user-level signal handling
* stack-frames in one go after that.
*/
static void do_signal(struct pt_regs *regs)
{
unsigned long continue_addr = 0, restart_addr = 0;
int retval = 0;
struct ksignal ksig;
bool syscall = in_syscall(regs);
/*
* If we were from a system call, check for system call restarting...
*/
if (syscall) {
continue_addr = regs->pc;
restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4);
retval = regs->regs[0];
/*
* Avoid additional syscall restarting via ret_to_user.
*/
forget_syscall(regs);
/*
* Prepare for system call restart. We do this here so that a
* debugger will see the already changed PC.
*/
switch (retval) {
case -ERESTARTNOHAND:
case -ERESTARTSYS:
case -ERESTARTNOINTR:
case -ERESTART_RESTARTBLOCK:
regs->regs[0] = regs->orig_x0;
regs->pc = restart_addr;
break;
}
}
/*
* Get the signal to deliver. When running under ptrace, at this point
* the debugger may change all of our registers.
*/
if (get_signal(&ksig)) {
/*
* Depending on the signal settings, we may need to revert the
* decision to restart the system call, but skip this if a
* debugger has chosen to restart at a different PC.
*/
if (regs->pc == restart_addr &&
(retval == -ERESTARTNOHAND ||
retval == -ERESTART_RESTARTBLOCK ||
(retval == -ERESTARTSYS &&
!(ksig.ka.sa.sa_flags & SA_RESTART)))) {
syscall_set_return_value(current, regs, -EINTR, 0);
regs->pc = continue_addr;
}
handle_signal(&ksig, regs);
return;
}
/*
* Handle restarting a different system call. As above, if a debugger
* has chosen to restart at a different PC, ignore the restart.
*/
if (syscall && regs->pc == restart_addr) {
if (retval == -ERESTART_RESTARTBLOCK)
setup_restart_syscall(regs);
user_rewind_single_step(current);
}
restore_saved_sigmask();
}
void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
{
do {
if (thread_flags & _TIF_NEED_RESCHED) {
/* Unmask Debug and SError for the next task */
local_daif_restore(DAIF_PROCCTX_NOIRQ);
schedule();
} else {
local_daif_restore(DAIF_PROCCTX);
if (thread_flags & _TIF_UPROBE)
uprobe_notify_resume(regs);
if (thread_flags & _TIF_MTE_ASYNC_FAULT) {
clear_thread_flag(TIF_MTE_ASYNC_FAULT);
send_sig_fault(SIGSEGV, SEGV_MTEAERR,
(void __user *)NULL, current);
}
if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
do_signal(regs);
if (thread_flags & _TIF_NOTIFY_RESUME)
tracehook_notify_resume(regs);
if (thread_flags & _TIF_FOREIGN_FPSTATE)
fpsimd_restore_current_state();
}
local_daif_mask();
thread_flags = READ_ONCE(current_thread_info()->flags);
} while (thread_flags & _TIF_WORK_MASK);
}
unsigned long __ro_after_init signal_minsigstksz;
/*
* Determine the stack space required for guaranteed signal devliery.
* This function is used to populate AT_MINSIGSTKSZ at process startup.
* cpufeatures setup is assumed to be complete.
*/
void __init minsigstksz_setup(void)
{
struct rt_sigframe_user_layout user;
init_user_layout(&user);
/*
* If this fails, SIGFRAME_MAXSZ needs to be enlarged. It won't
* be big enough, but it's our best guess:
*/
if (WARN_ON(setup_sigframe_layout(&user, true)))
return;
signal_minsigstksz = sigframe_size(&user) +
round_up(sizeof(struct frame_record), 16) +
16; /* max alignment padding */
}
/*
* Compile-time assertions for siginfo_t offsets. Check NSIG* as well, as
* changes likely come with new fields that should be added below.
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
static_assert(NSIGSEGV == 9);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
static_assert(NSIGSYS == 2);
static_assert(sizeof(siginfo_t) == 128);
static_assert(__alignof__(siginfo_t) == 8);
static_assert(offsetof(siginfo_t, si_signo) == 0x00);
static_assert(offsetof(siginfo_t, si_errno) == 0x04);
static_assert(offsetof(siginfo_t, si_code) == 0x08);
static_assert(offsetof(siginfo_t, si_pid) == 0x10);
static_assert(offsetof(siginfo_t, si_uid) == 0x14);
static_assert(offsetof(siginfo_t, si_tid) == 0x10);
static_assert(offsetof(siginfo_t, si_overrun) == 0x14);
static_assert(offsetof(siginfo_t, si_status) == 0x18);
static_assert(offsetof(siginfo_t, si_utime) == 0x20);
static_assert(offsetof(siginfo_t, si_stime) == 0x28);
static_assert(offsetof(siginfo_t, si_value) == 0x18);
static_assert(offsetof(siginfo_t, si_int) == 0x18);
static_assert(offsetof(siginfo_t, si_ptr) == 0x18);
static_assert(offsetof(siginfo_t, si_addr) == 0x10);
static_assert(offsetof(siginfo_t, si_addr_lsb) == 0x18);
static_assert(offsetof(siginfo_t, si_lower) == 0x20);
static_assert(offsetof(siginfo_t, si_upper) == 0x28);
static_assert(offsetof(siginfo_t, si_pkey) == 0x20);
static_assert(offsetof(siginfo_t, si_perf_data) == 0x18);
static_assert(offsetof(siginfo_t, si_perf_type) == 0x20);
static_assert(offsetof(siginfo_t, si_perf_flags) == 0x24);
static_assert(offsetof(siginfo_t, si_band) == 0x10);
static_assert(offsetof(siginfo_t, si_fd) == 0x18);
static_assert(offsetof(siginfo_t, si_call_addr) == 0x10);
static_assert(offsetof(siginfo_t, si_syscall) == 0x18);
static_assert(offsetof(siginfo_t, si_arch) == 0x1c);
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