arm64: convert syscall trace logic to C

Currently syscall tracing is a tricky assembly state machine, which can
be rather difficult to follow, and even harder to modify. Before we
start fiddling with it for pt_regs syscalls, let's convert it to C.

This is not intended to have any functional change.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Mark Rutland 2018-07-11 14:56:44 +01:00 committed by Will Deacon
parent 4141c857fd
commit f37099b699
2 changed files with 56 additions and 56 deletions

View File

@ -896,26 +896,6 @@ el0_error_naked:
b ret_to_user
ENDPROC(el0_error)
/*
* This is the fast syscall return path. We do as little as possible here,
* and this includes saving x0 back into the kernel stack.
*/
ret_fast_syscall:
disable_daif
#ifndef CONFIG_DEBUG_RSEQ
ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
enable_step_tsk x1, x2
kernel_exit 0
#endif
ret_fast_syscall_trace:
enable_daif
b __sys_trace_return_skipped // we already saved x0
/*
* Ok, we need to do extra processing, enter the slow path.
*/
@ -971,44 +951,13 @@ alternative_else_nop_endif
#endif
el0_svc_naked: // compat entry point
stp x0, xscno, [sp, #S_ORIG_X0] // save the original x0 and syscall number
enable_daif
ct_user_exit 1
tst x16, #_TIF_SYSCALL_WORK // check for syscall hooks
b.ne __sys_trace
mov x0, sp
mov w1, wscno
mov w2, wsc_nr
mov x3, stbl
bl invoke_syscall
b ret_fast_syscall
ENDPROC(el0_svc)
/*
* This is the really slow path. We're going to be doing context
* switches, and waiting for our parent to respond.
*/
__sys_trace:
cmp wscno, #NO_SYSCALL // user-issued syscall(-1)?
b.ne 1f
mov x0, #-ENOSYS // set default errno if so
str x0, [sp, #S_X0]
1: mov x0, sp
bl syscall_trace_enter
cmp w0, #NO_SYSCALL // skip the syscall?
b.eq __sys_trace_return_skipped
mov x0, sp
mov w1, wscno
mov w2, wsc_nr
mov x3, stbl
bl invoke_syscall
__sys_trace_return_skipped:
mov x0, sp
bl syscall_trace_exit
bl el0_svc_common
b ret_to_user
ENDPROC(el0_svc)
.popsection // .entry.text

View File

@ -1,11 +1,15 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/compiler.h>
#include <linux/context_tracking.h>
#include <linux/errno.h>
#include <linux/nospec.h>
#include <linux/ptrace.h>
#include <linux/syscalls.h>
#include <asm/daifflags.h>
#include <asm/syscall.h>
#include <asm/thread_info.h>
long compat_arm_syscall(struct pt_regs *regs);
@ -29,9 +33,9 @@ static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
regs->regs[3], regs->regs[4], regs->regs[5]);
}
asmlinkage void invoke_syscall(struct pt_regs *regs, unsigned int scno,
unsigned int sc_nr,
const syscall_fn_t syscall_table[])
static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
unsigned int sc_nr,
const syscall_fn_t syscall_table[])
{
long ret;
@ -45,3 +49,50 @@ asmlinkage void invoke_syscall(struct pt_regs *regs, unsigned int scno,
regs->regs[0] = ret;
}
static inline bool has_syscall_work(unsigned long flags)
{
return unlikely(flags & _TIF_SYSCALL_WORK);
}
int syscall_trace_enter(struct pt_regs *regs);
void syscall_trace_exit(struct pt_regs *regs);
asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
const syscall_fn_t syscall_table[])
{
unsigned long flags = current_thread_info()->flags;
regs->orig_x0 = regs->regs[0];
regs->syscallno = scno;
local_daif_restore(DAIF_PROCCTX);
user_exit();
if (has_syscall_work(flags)) {
/* set default errno for user-issued syscall(-1) */
if (scno == NO_SYSCALL)
regs->regs[0] = -ENOSYS;
scno = syscall_trace_enter(regs);
if (scno == NO_SYSCALL)
goto trace_exit;
}
invoke_syscall(regs, scno, sc_nr, syscall_table);
/*
* The tracing status may have changed under our feet, so we have to
* check again. However, if we were tracing entry, then we always trace
* exit regardless, as the old entry assembly did.
*/
if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
local_daif_mask();
flags = current_thread_info()->flags;
if (!has_syscall_work(flags))
return;
local_daif_restore(DAIF_PROCCTX);
}
trace_exit:
syscall_trace_exit(regs);
}