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x86/cet: Sync with Linux kernel 6.6 shadow stack interface

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Sync with Linux kernel 6.6 shadow stack interface.  Since only x86-64 is
supported, i386 shadow stack codes are unchanged and CET shouldn't be
enabled for i386.

1. When the shadow stack base in TCB is unset, the default shadow stack
is in use.  Use the current shadow stack pointer as the marker for the
default shadow stack. It is used to identify if the current shadow stack
is the same as the target shadow stack when switching ucontexts.  If yes,
INCSSP will be used to unwind shadow stack.  Otherwise, shadow stack
restore token will be used.
2. Allocate shadow stack with the map_shadow_stack syscall.  Since there
is no function to explicitly release ucontext, there is no place to
release shadow stack allocated by map_shadow_stack in ucontext functions.
Such shadow stacks will be leaked.
3. Rename arch_prctl CET commands to ARCH_SHSTK_XXX.
4. Rewrite the CET control functions with the current kernel shadow stack
interface.

Since CET is no longer enabled by kernel, a separate patch will enable
shadow stack during startup.
This commit is contained in:
H.J. Lu 2023-12-29 08:43:49 -08:00
parent 6b32696116
commit edb5e0c8f9
15 changed files with 173 additions and 133 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
sysdeps/unix/sysv/linux/x86/bits/mman.h
View File

@ -27,6 +27,11 @@
#define MAP_32BIT 0x40 /* Only give out 32-bit addresses. */
#define MAP_ABOVE4G 0x80 /* Only map above 4GB. */
#ifdef __USE_MISC
/* Set up a restore token in the newly allocated shadow stack */
# define SHADOW_STACK_SET_TOKEN 0x1
#endif
#include <bits/mman-map-flags-generic.h>
/* Include generic Linux declarations. */

13
sysdeps/unix/sysv/linux/x86/cpu-features.c
View File

@ -23,10 +23,15 @@
static inline int __attribute__ ((always_inline))
get_cet_status (void)
{
unsigned long long cet_status[3];
if (INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_CET_STATUS, cet_status) == 0)
return cet_status[0];
return 0;
unsigned long long kernel_feature;
unsigned int status = 0;
if (INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_STATUS,
&kernel_feature) == 0)
{
if ((kernel_feature & ARCH_SHSTK_SHSTK) != 0)
status = GNU_PROPERTY_X86_FEATURE_1_SHSTK;
}
return status;
}
# ifndef SHARED

16
sysdeps/unix/sysv/linux/x86/dl-cet.h
View File

@ -21,12 +21,20 @@
static inline int __attribute__ ((always_inline))
dl_cet_disable_cet (unsigned int cet_feature)
{
return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_CET_DISABLE,
cet_feature);
if (cet_feature != GNU_PROPERTY_X86_FEATURE_1_SHSTK)
return -1;
long long int kernel_feature = ARCH_SHSTK_SHSTK;
return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_DISABLE,
kernel_feature);
}
static inline int __attribute__ ((always_inline))
dl_cet_lock_cet (void)
dl_cet_lock_cet (unsigned int cet_feature)
{
return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_CET_LOCK, 0);
if (cet_feature != GNU_PROPERTY_X86_FEATURE_1_SHSTK)
return -1;
/* Lock all SHSTK features. */
long long int kernel_feature = -1;
return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_LOCK,
kernel_feature);
}

37
sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
View File

@ -4,24 +4,19 @@
#include_next <asm/prctl.h>
#ifndef ARCH_CET_STATUS
/* CET features:
IBT: GNU_PROPERTY_X86_FEATURE_1_IBT
SHSTK: GNU_PROPERTY_X86_FEATURE_1_SHSTK
*/
/* Return CET features in unsigned long long *addr:
features: addr[0].
shadow stack base address: addr[1].
shadow stack size: addr[2].
*/
# define ARCH_CET_STATUS 0x3001
/* Disable CET features in unsigned int features. */
# define ARCH_CET_DISABLE 0x3002
/* Lock all CET features. */
# define ARCH_CET_LOCK 0x3003
/* Allocate a new shadow stack with unsigned long long *addr:
IN: requested shadow stack size: *addr.
OUT: allocated shadow stack address: *addr.
*/
# define ARCH_CET_ALLOC_SHSTK 0x3004
#endif /* ARCH_CET_STATUS */
#ifndef ARCH_SHSTK_ENABLE
/* Enable SHSTK features in unsigned long int features. */
# define ARCH_SHSTK_ENABLE 0x5001
/* Disable SHSTK features in unsigned long int features. */
# define ARCH_SHSTK_DISABLE 0x5002
/* Lock SHSTK features in unsigned long int features. */
# define ARCH_SHSTK_LOCK 0x5003
/* Unlock SHSTK features in unsigned long int features. */
# define ARCH_SHSTK_UNLOCK 0x5004
/* Return SHSTK features in unsigned long int features. */
# define ARCH_SHSTK_STATUS 0x5005
/* ARCH_SHSTK_ features bits */
# define ARCH_SHSTK_SHSTK 0x1
# define ARCH_SHSTK_WRSS 0x2
#endif

17
sysdeps/unix/sysv/linux/x86/tst-cet-setcontext-1.c
View File

@ -87,15 +87,14 @@ do_test (void)
ctx[4].uc_link = &ctx[0];
makecontext (&ctx[4], (void (*) (void)) f1, 0);
/* NB: When shadow stack is enabled, makecontext calls arch_prctl
with ARCH_CET_ALLOC_SHSTK to allocate a new shadow stack which
can be unmapped. The base address and size of the new shadow
stack are returned in __ssp[1] and __ssp[2]. makecontext is
called for CTX1, CTX3 and CTX4. But only CTX1 is used. New
shadow stacks are allocated in the order of CTX3, CTX1, CTX4.
It is very likely that CTX1's shadow stack is placed between
CTX3 and CTX4. We munmap CTX3's and CTX4's shadow stacks to
create gaps above and below CTX1's shadow stack. We check
/* NB: When shadow stack is enabled, makecontext calls map_shadow_stack
to allocate a new shadow stack which can be unmapped. The base
address and size of the new shadow stack are returned in __ssp[1]
and __ssp[2]. makecontext is called for CTX1, CTX3 and CTX4. But
only CTX1 is used. New shadow stacks are allocated in the order
of CTX3, CTX1, CTX4. It is very likely that CTX1's shadow stack is
placed between CTX3 and CTX4. We munmap CTX3's and CTX4's shadow
stacks to create gaps above and below CTX1's shadow stack. We check
that setcontext CTX1 works correctly in this case. */
if (_get_ssp () != 0)
{

2
sysdeps/unix/sysv/linux/x86_64/Makefile
View File

@ -3,7 +3,7 @@ sysdep_routines += ioperm iopl
endif
ifeq ($(subdir),stdlib)
sysdep_routines += __start_context
sysdep_routines += __start_context allocate-shadow-stack
endif
ifeq ($(subdir),csu)

38
sysdeps/unix/sysv/linux/x86_64/__start_context.S
View File

@ -24,20 +24,14 @@
/* Use CALL to push __start_context onto the new stack as well as the new
shadow stack. RDI points to ucontext:
Incoming:
__ssp[0]: The original caller's shadow stack pointer.
__ssp[1]: The size of the new shadow stack.
__ssp[2]: The size of the new shadow stack.
Outgoing:
__ssp[0]: The new shadow stack pointer.
__ssp[1]: The base address of the new shadow stack.
__ssp[2]: The size of the new shadow stack.
*/
ENTRY(__push___start_context)
/* Save the pointer to ucontext. */
movq %rdi, %r9
/* Get the original shadow stack pointer. */
rdsspq %r8
rdsspq %rcx
/* Save the original stack pointer. */
movq %rsp, %rdx
/* Load the top of the new stack into RSI. */
@ -45,24 +39,12 @@ ENTRY(__push___start_context)
/* Add 8 bytes to RSI since CALL will push the 8-byte return
address onto stack. */
leaq 8(%rsi), %rsp
/* Allocate the new shadow stack. The size of the new shadow
stack is passed in __ssp[1]. */
lea (oSSP + 8)(%rdi), %RSI_LP
movl $ARCH_CET_ALLOC_SHSTK, %edi
movl $__NR_arch_prctl, %eax
/* The new shadow stack base is returned in __ssp[1]. */
syscall
testq %rax, %rax
jne L(hlt) /* This should never happen. */
/* Get the size of the new shadow stack. */
movq 8(%rsi), %rdi
/* Get the base address of the new shadow stack. */
movq (%rsi), %rsi
/* The size of the new shadow stack is stored in __ssp[2]. */
mov (oSSP + 16)(%rdi), %RSI_LP
/* The new shadow stack base is stored in __ssp[1]. */
mov (oSSP + 8)(%rdi), %RAX_LP
/* Use the restore stoken to restore the new shadow stack. */
rstorssp -8(%rsi, %rdi)
rstorssp -8(%rax, %rsi)
/* Save the restore token on the original shadow stack. */
saveprevssp
@ -73,18 +55,12 @@ ENTRY(__push___start_context)
jmp __start_context
1:
/* Get the new shadow stack pointer. */
rdsspq %rdi
/* Use the restore stoken to restore the original shadow stack. */
rstorssp -8(%r8)
rstorssp -8(%rcx)
/* Save the restore token on the new shadow stack. */
saveprevssp
/* Store the new shadow stack pointer in __ssp[0]. */
movq %rdi, oSSP(%r9)
/* Restore the original stack. */
mov %rdx, %rsp
ret

55
sysdeps/unix/sysv/linux/x86_64/allocate-shadow-stack.c Normal file
View File

@ -0,0 +1,55 @@
/* Helper function to allocate shadow stack.
Copyright (C) 2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <stdint.h>
#include <errno.h>
#include <sys/mman.h>
#include <libc-pointer-arith.h>
#include <allocate-shadow-stack.h>
/* NB: This can be treated as a syscall by caller. */
long int
__allocate_shadow_stack (size_t stack_size,
shadow_stack_size_t *child_stack)
{
#ifdef __NR_map_shadow_stack
size_t shadow_stack_size
= stack_size >> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT;
/* Align shadow stack to 8 bytes. */
shadow_stack_size = ALIGN_UP (shadow_stack_size, 8);
/* Since sigaltstack shares shadow stack with the current context in
the thread, add extra 20 stack frames in shadow stack for signal
handlers. */
shadow_stack_size += 20 * 8;
void *shadow_stack = (void *)INLINE_SYSCALL_CALL
(map_shadow_stack, NULL, shadow_stack_size, SHADOW_STACK_SET_TOKEN);
/* Report the map_shadow_stack error. */
if (shadow_stack == MAP_FAILED)
return -errno;
/* Save the shadow stack base and size on child stack. */
child_stack[0] = (uintptr_t) shadow_stack;
child_stack[1] = shadow_stack_size;
return 0;
#else
return -ENOSYS;
#endif
}

24
sysdeps/unix/sysv/linux/x86_64/allocate-shadow-stack.h Normal file
View File

@ -0,0 +1,24 @@
/* Helper function to allocate shadow stack.
Copyright (C) 2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <ucontext.h>
typedef __typeof (((ucontext_t *) 0)->__ssp[0]) shadow_stack_size_t;
extern long int __allocate_shadow_stack (size_t, shadow_stack_size_t *)
attribute_hidden;

30
sysdeps/unix/sysv/linux/x86_64/getcontext.S
View File

@ -58,35 +58,15 @@ ENTRY(__getcontext)
testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
jz L(no_shstk)
/* Save RDI in RDX which won't be clobbered by syscall. */
movq %rdi, %rdx
xorl %eax, %eax
cmpq %fs:SSP_BASE_OFFSET, %rax
jnz L(shadow_stack_bound_recorded)
/* Get the base address and size of the default shadow stack
which must be the current shadow stack since nothing has
been recorded yet. */
sub $24, %RSP_LP
mov %RSP_LP, %RSI_LP
movl $ARCH_CET_STATUS, %edi
movl $__NR_arch_prctl, %eax
syscall
testq %rax, %rax
jz L(continue_no_err)
/* This should never happen. */
hlt
L(continue_no_err):
/* Record the base of the current shadow stack. */
movq 8(%rsp), %rax
/* When the shadow stack base is unset, the default shadow
stack is in use. Use the current shadow stack pointer
as the marker for the default shadow stack. */
rdsspq %rax
movq %rax, %fs:SSP_BASE_OFFSET
add $24, %RSP_LP
/* Restore RDI. */
movq %rdx, %rdi
L(shadow_stack_bound_recorded):
/* Get the current shadow stack pointer. */
@ -94,7 +74,7 @@ L(shadow_stack_bound_recorded):
/* NB: Save the caller's shadow stack so that we can jump back
to the caller directly. */
addq $8, %rax
movq %rax, oSSP(%rdx)
movq %rax, oSSP(%rdi)
/* Save the current shadow stack base in ucontext. */
movq %fs:SSP_BASE_OFFSET, %rax

28
sysdeps/unix/sysv/linux/x86_64/makecontext.c
View File

@ -24,6 +24,7 @@
# include <pthread.h>
# include <libc-pointer-arith.h>
# include <sys/prctl.h>
# include <allocate-shadow-stack.h>
#endif
#include "ucontext_i.h"
@ -88,23 +89,24 @@ __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
if ((feature_1 & X86_FEATURE_1_SHSTK) != 0)
{
/* Shadow stack is enabled. We need to allocate a new shadow
stack. */
unsigned long ssp_size = (((uintptr_t) sp
- (uintptr_t) ucp->uc_stack.ss_sp)
>> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT);
/* Align shadow stack to 8 bytes. */
ssp_size = ALIGN_UP (ssp_size, 8);
ucp->__ssp[1] = ssp_size;
ucp->__ssp[2] = ssp_size;
/* Call __push___start_context to allocate a new shadow stack,
push __start_context onto the new stack as well as the new
shadow stack. NB: After __push___start_context returns,
stack. NB:
ucp->__ssp[0]: The new shadow stack pointer.
ucp->__ssp[1]: The base address of the new shadow stack.
ucp->__ssp[2]: The size of the new shadow stack.
*/
long int ret
= __allocate_shadow_stack (((uintptr_t) sp
- (uintptr_t) ucp->uc_stack.ss_sp),
&ucp->__ssp[1]);
if (ret != 0)
{
/* FIXME: What should we do? */
abort ();
}
ucp->__ssp[0] = ucp->__ssp[1] + ucp->__ssp[2] - 8;
/* Call __push___start_context to push __start_context onto the new
stack as well as the new shadow stack. */
__push___start_context (ucp);
}
else

22
sysdeps/unix/sysv/linux/x86_64/swapcontext.S
View File

@ -109,25 +109,11 @@ ENTRY(__swapcontext)
cmpq %fs:SSP_BASE_OFFSET, %rax
jnz L(shadow_stack_bound_recorded)
/* Get the base address and size of the default shadow stack
which must be the current shadow stack since nothing has
been recorded yet. */
sub $24, %RSP_LP
mov %RSP_LP, %RSI_LP
movl $ARCH_CET_STATUS, %edi
movl $__NR_arch_prctl, %eax
syscall
testq %rax, %rax
jz L(continue_no_err)
/* This should never happen. */
hlt
L(continue_no_err):
/* Record the base of the current shadow stack. */
movq 8(%rsp), %rax
/* When the shadow stack base is unset, the default shadow
stack is in use. Use the current shadow stack pointer
as the marker for the default shadow stack. */
rdsspq %rax
movq %rax, %fs:SSP_BASE_OFFSET
add $24, %RSP_LP
L(shadow_stack_bound_recorded):
/* If we unwind the stack, we can't undo stack unwinding. Just

15
sysdeps/x86/cpu-features.c
View File

@ -1121,8 +1121,9 @@ no_cpuid:
# ifndef SHARED
/* Check if IBT and SHSTK are enabled by kernel. */
if ((cet_status & GNU_PROPERTY_X86_FEATURE_1_IBT)
|| (cet_status & GNU_PROPERTY_X86_FEATURE_1_SHSTK))
if ((cet_status
& (GNU_PROPERTY_X86_FEATURE_1_IBT
| GNU_PROPERTY_X86_FEATURE_1_SHSTK)))
{
/* Disable IBT and/or SHSTK if they are enabled by kernel, but
disabled by environment variable:
@ -1131,9 +1132,11 @@ no_cpuid:
*/
unsigned int cet_feature = 0;
if (!CPU_FEATURE_USABLE (IBT))
cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
cet_feature |= (cet_status
& GNU_PROPERTY_X86_FEATURE_1_IBT);
if (!CPU_FEATURE_USABLE (SHSTK))
cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
cet_feature |= (cet_status
& GNU_PROPERTY_X86_FEATURE_1_SHSTK);
if (cet_feature)
{
@ -1148,7 +1151,9 @@ no_cpuid:
lock CET if IBT or SHSTK is enabled permissively. */
if (GL(dl_x86_feature_control).ibt != cet_permissive
&& GL(dl_x86_feature_control).shstk != cet_permissive)
dl_cet_lock_cet ();
dl_cet_lock_cet (GL(dl_x86_feature_1)
& (GNU_PROPERTY_X86_FEATURE_1_IBT
| GNU_PROPERTY_X86_FEATURE_1_SHSTK));
}
# endif
}

2
sysdeps/x86/dl-cet.c
View File

@ -202,7 +202,7 @@ dl_cet_check_startup (struct link_map *m, struct dl_cet_info *info)
feature_1_lock |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
if (feature_1_lock != 0
&& dl_cet_lock_cet () != 0)
&& dl_cet_lock_cet (feature_1_lock) != 0)
_dl_fatal_printf ("%s: can't lock CET\n", info->program);
}

2
sysdeps/x86_64/nptl/tls.h
View File

@ -60,7 +60,7 @@ typedef struct
void *__private_tm[4];
/* GCC split stack support. */
void *__private_ss;
/* The lowest address of shadow stack, */
/* The marker for the current shadow stack. */
unsigned long long int ssp_base;
/* Must be kept even if it is no longer used by glibc since programs,
like AddressSanitizer, depend on the size of tcbhead_t. */