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Re: V2: [PATCH 02/24] x86: Support shadow stack pointer in setjmp/longjmp
- From: Carlos O'Donell <carlos at redhat dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Fri, 13 Jul 2018 14:49:01 -0400
- Subject: Re: V2: [PATCH 02/24] x86: Support shadow stack pointer in setjmp/longjmp
- References: <20180613153207.57232-1-hjl.tools@gmail.com> <20180613153207.57232-3-hjl.tools@gmail.com> <abc02573-7240-e248-9bfe-bdc324b9e07d@redhat.com> <20180713132252.GC2606@gmail.com>
On 07/13/2018 09:22 AM, H.J. Lu wrote:
> On Thu, Jul 12, 2018 at 02:13:21PM -0400, Carlos O'Donell wrote:
>> On 06/13/2018 11:31 AM, H.J. Lu wrote:
>>> Save and restore shadow stack pointer in setjmp and longjmp to support
>>> shadow stack in Intel CET. Use feature_1 in tcbhead_t to check if
>>> shadow stack is enabled before saving and restoring shadow stack
>>> pointer so that it works with the old smaller cancel_jmp_buf which
>>> doesn't have space for shadow stack pointer.
>>
>> This comment can't be accurate. For the older smaller cancel_jmp_buf
>> we found another way to solve this because you just don't restore the
>> shadowstack since we're jumping out through the unwinder. So we only
>> need this logically for setjmp/longjmp and *context functions?
>>
>> In general this is OK, I'd like to see a v2:
>>
>> - New accurate commit message.
>> - Replace (1 << 1) with meaningful macro constants that help a future
>> reader identify which FEATURE_1 flag we're looking at.
>>
>
> Done.
>
> ...
>>>
>>> +# ifdef SHADOW_STACK_POINTER_OFFSET
>>> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
>>> + /* Check if Shadow Stack is enabled. */
>>> + testl $(1 << 1), %gs:FEATURE_1_OFFSET
>>
>> Please replace all instances of "1" here with some kind of macro
>> that actually defines which flag we're checking.
>>
>
> I updated [PATCH 01/24] to add X86_FEATURE_1_IBT and X86_FEATURE_1_SHSTK
> in
>
> https://sourceware.org/ml/libc-alpha/2018-07/msg00375.html
>
> Here is the V2 patch. OK for master?
This is OK for master and 2.28.
Thanks for the update and cleanups.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
>
> H.J.
> ----
> Save and restore shadow stack pointer in setjmp and longjmp to support
> shadow stack in Intel CET. Use feature_1 in tcbhead_t to check if
> shadow stack is enabled before saving and restoring shadow stack pointer.
>
> 2017-12-07 Igor Tsimbalist <igor.v.tsimbalist@intel.com>
> H.J. Lu <hongjiu.lu@intel.com>
>
> * sysdeps/i386/__longjmp.S: Include <jmp_buf-ssp.h>.
> (__longjmp): Restore shadow stack pointer if shadow stack is
> enabled, SHADOW_STACK_POINTER_OFFSET is defined and __longjmp
> isn't defined for __longjmp_cancel.
> * sysdeps/i386/bsd-_setjmp.S: Include <jmp_buf-ssp.h>.
> (_setjmp): Save shadow stack pointer if shadow stack is enabled
> and SHADOW_STACK_POINTER_OFFSET is defined.
> * sysdeps/i386/bsd-setjmp.S: Include <jmp_buf-ssp.h>.
> (setjmp): Save shadow stack pointer if shadow stack is enabled
> and SHADOW_STACK_POINTER_OFFSET is defined.
> * sysdeps/i386/setjmp.S: Include <jmp_buf-ssp.h>.
> (__sigsetjmp): Save shadow stack pointer if shadow stack is
> enabled and SHADOW_STACK_POINTER_OFFSET is defined.
> * sysdeps/unix/sysv/linux/i386/____longjmp_chk.S: Include
> <jmp_buf-ssp.h>.
> (____longjmp_chk): Restore shadow stack pointer if shadow stack
> is enabled and SHADOW_STACK_POINTER_OFFSET is defined.
> * sysdeps/unix/sysv/linux/x86/Makefile (gen-as-const-headers):
> Remove jmp_buf-ssp.sym.
> * sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S: Include
> <jmp_buf-ssp.h>.
> (____longjmp_chk): Restore shadow stack pointer if shadow stack
> is enabled and SHADOW_STACK_POINTER_OFFSET is defined.
> * sysdeps/x86/Makefile (gen-as-const-headers): Add
> jmp_buf-ssp.sym.
> * sysdeps/x86/jmp_buf-ssp.sym: New dummy file.
> * sysdeps/x86_64/__longjmp.S: Include <jmp_buf-ssp.h>.
> (__longjmp): Restore shadow stack pointer if shadow stack is
> enabled, SHADOW_STACK_POINTER_OFFSET is defined and __longjmp
> isn't defined for __longjmp_cancel.
> * sysdeps/x86_64/setjmp.S: Include <jmp_buf-ssp.h>.
> (__sigsetjmp): Save shadow stack pointer if shadow stack is
> enabled and SHADOW_STACK_POINTER_OFFSET is defined.
> ---
> sysdeps/i386/__longjmp.S | 73 +++++++++++++++++++
> sysdeps/i386/bsd-_setjmp.S | 21 ++++++
> sysdeps/i386/bsd-setjmp.S | 21 ++++++
> sysdeps/i386/setjmp.S | 21 ++++++
> .../unix/sysv/linux/i386/____longjmp_chk.S | 37 ++++++++++
> sysdeps/unix/sysv/linux/x86/Makefile | 1 -
> .../unix/sysv/linux/x86_64/____longjmp_chk.S | 38 ++++++++++
> sysdeps/x86/Makefile | 1 +
> sysdeps/x86/jmp_buf-ssp.sym | 1 +
> sysdeps/x86_64/__longjmp.S | 44 +++++++++++
> sysdeps/x86_64/setjmp.S | 21 ++++++
> 11 files changed, 278 insertions(+), 1 deletion(-)
> create mode 100644 sysdeps/x86/jmp_buf-ssp.sym
>
> diff --git a/sysdeps/i386/__longjmp.S b/sysdeps/i386/__longjmp.S
> index b38333bead..6e98ed538d 100644
> --- a/sysdeps/i386/__longjmp.S
> +++ b/sysdeps/i386/__longjmp.S
> @@ -18,14 +18,55 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <asm-syntax.h>
> #include <stap-probe.h>
>
> +/* Don't restore shadow stack register if
> + 1. Shadow stack isn't enabled. Or
> + 2. __longjmp is defined for __longjmp_cancel.
> + */
> +#if !SHSTK_ENABLED || defined __longjmp
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> .text
> ENTRY (__longjmp)
> #ifdef PTR_DEMANGLE
> movl 4(%esp), %eax /* User's jmp_buf in %eax. */
>
> +# ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %edx, %edx
> +# endif
> + /* Check and adjust the Shadow-Stack-Pointer. */
> + rdsspd %edx
> + /* And compare it with the saved ssp value. */
> + subl SHADOW_STACK_POINTER_OFFSET(%eax), %edx
> + je L(skip_ssp)
> + /* Count the number of frames to adjust and adjust it
> + with incssp instruction. The instruction can adjust
> + the ssp by [0..255] value only thus use a loop if
> + the number of frames is bigger than 255. */
> + negl %edx
> + shrl $2, %edx
> + /* NB: We saved Shadow-Stack-Pointer of setjmp. Since we are
> + restoring Shadow-Stack-Pointer of setjmp's caller, we
> + need to unwind shadow stack by one more frame. */
> + addl $1, %edx
> + movl $255, %ebx
> +L(loop):
> + cmpl %ebx, %edx
> + cmovb %edx, %ebx
> + incsspd %ebx
> + subl %ebx, %edx
> + ja L(loop)
> +L(skip_ssp):
> +# endif
> /* Save the return address now. */
> movl (JB_PC*4)(%eax), %edx
> /* Get the stack pointer. */
> @@ -56,6 +97,38 @@ ENTRY (__longjmp)
> #else
> movl 4(%esp), %ecx /* User's jmp_buf in %ecx. */
> movl 8(%esp), %eax /* Second argument is return value. */
> +# ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# endif
> + /* Check and adjust the Shadow-Stack-Pointer. */
> + xorl %edx, %edx
> + /* Get the current ssp. */
> + rdsspd %edx
> + /* And compare it with the saved ssp value. */
> + subl SHADOW_STACK_POINTER_OFFSET(%ecx), %edx
> + je L(skip_ssp)
> + /* Count the number of frames to adjust and adjust it
> + with incssp instruction. The instruction can adjust
> + the ssp by [0..255] value only thus use a loop if
> + the number of frames is bigger than 255. */
> + negl %edx
> + shrl $2, %edx
> + /* NB: We saved Shadow-Stack-Pointer of setjmp. Since we are
> + restoring Shadow-Stack-Pointer of setjmp's caller, we
> + need to unwind shadow stack by one more frame. */
> + addl $1, %edx
> + movl $255, %ebx
> +L(loop):
> + cmpl %ebx, %edx
> + cmovb %edx, %ebx
> + incsspd %ebx
> + subl %ebx, %edx
> + ja L(loop)
> +L(skip_ssp):
> +# endif
> /* Save the return address now. */
> movl (JB_PC*4)(%ecx), %edx
> LIBC_PROBE (longjmp, 3, 4@%ecx, -4@%eax, 4@%edx)
> diff --git a/sysdeps/i386/bsd-_setjmp.S b/sysdeps/i386/bsd-_setjmp.S
> index a626cc6d22..db47df0ba1 100644
> --- a/sysdeps/i386/bsd-_setjmp.S
> +++ b/sysdeps/i386/bsd-_setjmp.S
> @@ -22,12 +22,18 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <stap-probe.h>
>
> #define PARMS 4 /* no space for saved regs */
> #define JMPBUF PARMS
> #define SIGMSK JMPBUF+4
>
> +/* Don't save shadow stack register if shadow stack isn't enabled. */
> +#if !SHSTK_ENABLED
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> ENTRY (_setjmp)
>
> xorl %eax, %eax
> @@ -51,6 +57,21 @@ ENTRY (_setjmp)
> movl %ebp, (JB_BP*4)(%edx) /* Save caller's frame pointer. */
>
> movl %eax, JB_SIZE(%edx) /* No signal mask set. */
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %ecx, %ecx
> +# endif
> + /* Get the current Shadow-Stack-Pointer and save it. */
> + rdsspd %ecx
> + movl %ecx, SHADOW_STACK_POINTER_OFFSET(%edx)
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> +L(skip_ssp):
> +# endif
> +#endif
> ret
> END (_setjmp)
> libc_hidden_def (_setjmp)
> diff --git a/sysdeps/i386/bsd-setjmp.S b/sysdeps/i386/bsd-setjmp.S
> index 2da8b73c49..1290d0d82b 100644
> --- a/sysdeps/i386/bsd-setjmp.S
> +++ b/sysdeps/i386/bsd-setjmp.S
> @@ -22,12 +22,18 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <stap-probe.h>
>
> #define PARMS 4 /* no space for saved regs */
> #define JMPBUF PARMS
> #define SIGMSK JMPBUF+4
>
> +/* Don't save shadow stack register if shadow stack isn't enabled. */
> +#if !SHSTK_ENABLED
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> ENTRY (setjmp)
> /* Note that we have to use a non-exported symbol in the next
> jump since otherwise gas will emit it as a jump through the
> @@ -51,6 +57,21 @@ ENTRY (setjmp)
> #endif
> movl %ecx, (JB_PC*4)(%eax)
> movl %ebp, (JB_BP*4)(%eax) /* Save caller's frame pointer. */
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %ecx, %ecx
> +# endif
> + /* Get the current Shadow-Stack-Pointer and save it. */
> + rdsspd %ecx
> + movl %ecx, SHADOW_STACK_POINTER_OFFSET(%eax)
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> +L(skip_ssp):
> +# endif
> +#endif
>
> /* Call __sigjmp_save. */
> pushl $1
> diff --git a/sysdeps/i386/setjmp.S b/sysdeps/i386/setjmp.S
> index 6a08701717..889337b8ae 100644
> --- a/sysdeps/i386/setjmp.S
> +++ b/sysdeps/i386/setjmp.S
> @@ -18,6 +18,7 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <asm-syntax.h>
> #include <stap-probe.h>
>
> @@ -25,6 +26,11 @@
> #define JMPBUF PARMS
> #define SIGMSK JMPBUF+4
>
> +/* Don't save shadow stack register if shadow stack isn't enabled. */
> +#if !SHSTK_ENABLED
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> ENTRY (__sigsetjmp)
>
> movl JMPBUF(%esp), %eax
> @@ -46,6 +52,21 @@ ENTRY (__sigsetjmp)
> movl %ecx, (JB_PC*4)(%eax)
> movl %ebp, (JB_BP*4)(%eax) /* Save caller's frame pointer. */
>
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %ecx, %ecx
> +# endif
> + /* Get the current Shadow-Stack-Pointer and save it. */
> + rdsspd %ecx
> + movl %ecx, SHADOW_STACK_POINTER_OFFSET(%eax)
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> +L(skip_ssp):
> +# endif
> +#endif
> #if IS_IN (rtld)
> /* In ld.so we never save the signal mask. */
> xorl %eax, %eax
> diff --git a/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S b/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S
> index 3452433112..a7640d9892 100644
> --- a/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S
> +++ b/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S
> @@ -17,9 +17,14 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <asm-syntax.h>
> #include <stap-probe.h>
>
> +/* Don't restore shadow stack register if shadow stack isn't enabled. */
> +#if !SHSTK_ENABLED
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
>
> .section .rodata.str1.1,"aMS",@progbits,1
> .type longjmp_msg,@object
> @@ -46,6 +51,38 @@ longjmp_msg:
> ENTRY (____longjmp_chk)
> movl 4(%esp), %ecx /* User's jmp_buf in %ecx. */
>
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %edx, %edx
> +# endif
> + /* Check and adjust the Shadow-Stack-Pointer. */
> + rdsspd %edx
> + /* And compare it with the saved ssp value. */
> + subl SHADOW_STACK_POINTER_OFFSET(%ecx), %edx
> + je L(skip_ssp)
> + /* Count the number of frames to adjust and adjust it
> + with incssp instruction. The instruction can adjust
> + the ssp by [0..255] value only thus use a loop if
> + the number of frames is bigger than 255. */
> + negl %edx
> + shrl $2, %edx
> + /* NB: We saved Shadow-Stack-Pointer of setjmp. Since we are
> + restoring Shadow-Stack-Pointer of setjmp's caller, we
> + need to unwind shadow stack by one more frame. */
> + addl $1, %edx
> + movl $255, %ebx
> +L(loop):
> + cmpl %ebx, %edx
> + cmovb %edx, %ebx
> + incsspd %ebx
> + subl %ebx, %edx
> + ja L(loop)
> +L(skip_ssp):
> +#endif
> /* Save the return address now. */
> movl (JB_PC*4)(%ecx), %edx
> /* Get the stack pointer. */
> diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile
> index c55a43e58d..111ff9ff58 100644
> --- a/sysdeps/unix/sysv/linux/x86/Makefile
> +++ b/sysdeps/unix/sysv/linux/x86/Makefile
> @@ -21,6 +21,5 @@ sysdep_routines += dl-vdso
> endif
>
> ifeq ($(subdir),setjmp)
> -gen-as-const-headers += jmp_buf-ssp.sym
> tests += tst-saved_mask-1
> endif
> diff --git a/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S b/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S
> index 8a9f2e1a3c..7eb26fafca 100644
> --- a/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S
> +++ b/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S
> @@ -20,7 +20,13 @@
> #include <asm-syntax.h>
> #include <stap-probe.h>
>
> +/* Don't restore shadow stack register if shadow stack isn't enabled. */
> +#if !SHSTK_ENABLED
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> #include <sigaltstack-offsets.h>
> +#include <jmp_buf-ssp.h>
>
> .section .rodata.str1.1,"aMS",@progbits,1
> .type longjmp_msg,@object
> @@ -105,6 +111,38 @@ ENTRY(____longjmp_chk)
> cfi_restore (%rsi)
>
> .Lok:
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %eax, %eax
> +# endif
> + /* Check and adjust the Shadow-Stack-Pointer. */
> + rdsspq %rax
> + /* And compare it with the saved ssp value. */
> + subq SHADOW_STACK_POINTER_OFFSET(%rdi), %rax
> + je L(skip_ssp)
> + /* Count the number of frames to adjust and adjust it
> + with incssp instruction. The instruction can adjust
> + the ssp by [0..255] value only thus use a loop if
> + the number of frames is bigger than 255. */
> + negq %rax
> + shrq $3, %rax
> + /* NB: We saved Shadow-Stack-Pointer of setjmp. Since we are
> + restoring Shadow-Stack-Pointer of setjmp's caller, we
> + need to unwind shadow stack by one more frame. */
> + addq $1, %rax
> + movl $255, %ebx
> +L(loop):
> + cmpq %rbx, %rax
> + cmovb %rax, %rbx
> + incsspq %rbx
> + subq %rbx, %rax
> + ja L(loop)
> +L(skip_ssp):
> +#endif
> LIBC_PROBE (longjmp, 3, LP_SIZE@%RDI_LP, -4@%esi, LP_SIZE@%RDX_LP)
> /* We add unwind information for the target here. */
> cfi_def_cfa(%rdi, 0)
> diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
> index d25d6f0ae4..65292f4032 100644
> --- a/sysdeps/x86/Makefile
> +++ b/sysdeps/x86/Makefile
> @@ -10,5 +10,6 @@ tests-static += tst-get-cpu-features-static
> endif
>
> ifeq ($(subdir),setjmp)
> +gen-as-const-headers += jmp_buf-ssp.sym
> sysdep_routines += __longjmp_cancel
> endif
> diff --git a/sysdeps/x86/jmp_buf-ssp.sym b/sysdeps/x86/jmp_buf-ssp.sym
> new file mode 100644
> index 0000000000..1aaaedc9ec
> --- /dev/null
> +++ b/sysdeps/x86/jmp_buf-ssp.sym
> @@ -0,0 +1 @@
> +-- FIXME: Define SHADOW_STACK_POINTER_OFFSET to support shadow stack.
> diff --git a/sysdeps/x86_64/__longjmp.S b/sysdeps/x86_64/__longjmp.S
> index a487e0efd0..d7d123e4bc 100644
> --- a/sysdeps/x86_64/__longjmp.S
> +++ b/sysdeps/x86_64/__longjmp.S
> @@ -17,9 +17,18 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <asm-syntax.h>
> #include <stap-probe.h>
>
> +/* Don't restore shadow stack register if
> + 1. Shadow stack isn't enabled. Or
> + 2. __longjmp is defined for __longjmp_cancel.
> + */
> +#if !SHSTK_ENABLED || defined __longjmp
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> /* Jump to the position specified by ENV, causing the
> setjmp call there to return VAL, or 1 if VAL is 0.
> void __longjmp (__jmp_buf env, int val). */
> @@ -41,6 +50,41 @@ ENTRY(__longjmp)
> shlq $32, %rax
> orq %rax, %r9
> # endif
> +#endif
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %eax, %eax
> +# endif
> + /* Check and adjust the Shadow-Stack-Pointer. */
> + /* Get the current ssp. */
> + rdsspq %rax
> + /* And compare it with the saved ssp value. */
> + subq SHADOW_STACK_POINTER_OFFSET(%rdi), %rax
> + je L(skip_ssp)
> + /* Count the number of frames to adjust and adjust it
> + with incssp instruction. The instruction can adjust
> + the ssp by [0..255] value only thus use a loop if
> + the number of frames is bigger than 255. */
> + negq %rax
> + shrq $3, %rax
> + /* NB: We saved Shadow-Stack-Pointer of setjmp. Since we are
> + restoring Shadow-Stack-Pointer of setjmp's caller, we
> + need to unwind shadow stack by one more frame. */
> + addq $1, %rax
> +
> + movl $255, %ebx
> +L(loop):
> + cmpq %rbx, %rax
> + cmovb %rax, %rbx
> + incsspq %rbx
> + subq %rbx, %rax
> + ja L(loop)
> +
> +L(skip_ssp):
> #endif
> LIBC_PROBE (longjmp, 3, LP_SIZE@%RDI_LP, -4@%esi, LP_SIZE@%RDX_LP)
> /* We add unwind information for the target here. */
> diff --git a/sysdeps/x86_64/setjmp.S b/sysdeps/x86_64/setjmp.S
> index e0a648e3e4..78a8bf4644 100644
> --- a/sysdeps/x86_64/setjmp.S
> +++ b/sysdeps/x86_64/setjmp.S
> @@ -18,9 +18,15 @@
>
> #include <sysdep.h>
> #include <jmpbuf-offsets.h>
> +#include <jmp_buf-ssp.h>
> #include <asm-syntax.h>
> #include <stap-probe.h>
>
> +/* Don't save shadow stack register if shadow stack isn't enabled. */
> +#if !SHSTK_ENABLED
> +# undef SHADOW_STACK_POINTER_OFFSET
> +#endif
> +
> ENTRY (__sigsetjmp)
> /* Save registers. */
> movq %rbx, (JB_RBX*8)(%rdi)
> @@ -54,6 +60,21 @@ ENTRY (__sigsetjmp)
> #endif
> movq %rax, (JB_PC*8)(%rdi)
>
> +#ifdef SHADOW_STACK_POINTER_OFFSET
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> + /* Check if Shadow Stack is enabled. */
> + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
> + jz L(skip_ssp)
> +# else
> + xorl %eax, %eax
> +# endif
> + /* Get the current Shadow-Stack-Pointer and save it. */
> + rdsspq %rax
> + movq %rax, SHADOW_STACK_POINTER_OFFSET(%rdi)
> +# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
> +L(skip_ssp):
> +# endif
> +#endif
> #if IS_IN (rtld)
> /* In ld.so we never save the signal mask. */
> xorl %eax, %eax
>