diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/x86_64/setcontext.S')
| -rw-r--r-- | sysdeps/unix/sysv/linux/x86_64/setcontext.S | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/x86_64/setcontext.S b/sysdeps/unix/sysv/linux/x86_64/setcontext.S index b42af8e291..0afdf8ce0a 100644 --- a/sysdeps/unix/sysv/linux/x86_64/setcontext.S +++ b/sysdeps/unix/sysv/linux/x86_64/setcontext.S @@ -18,6 +18,7 @@ <http://www.gnu.org/licenses/>. */ #include <sysdep.h> +#include <asm/prctl.h> #include "ucontext_i.h" @@ -79,6 +80,97 @@ ENTRY(__setcontext) movq oR14(%rdx), %r14 movq oR15(%rdx), %r15 +#if SHSTK_ENABLED + /* Check if shadow stack is enabled. */ + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET + jz L(no_shstk) + + /* If the base of the target shadow stack is the same as the + base of the current shadow stack, we unwind the shadow + stack. Otherwise it is a stack switch and we look for a + restore token. */ + movq oSSP(%rdx), %rsi + movq %rsi, %rdi + + /* Get the base of the target shadow stack. */ + movq (oSSP + 8)(%rdx), %rcx + cmpq %fs:SSP_BASE_OFFSET, %rcx + je L(unwind_shadow_stack) + +L(find_restore_token_loop): + /* Look for a restore token. */ + movq -8(%rsi), %rax + andq $-8, %rax + cmpq %rsi, %rax + je L(restore_shadow_stack) + + /* Try the next slot. */ + subq $8, %rsi + jmp L(find_restore_token_loop) + +L(restore_shadow_stack): + /* Pop return address from the shadow stack since setcontext + will not return. */ + movq $1, %rax + incsspq %rax + + /* Use the restore stoken to restore the target shadow stack. */ + rstorssp -8(%rsi) + + /* Save the restore token on the old shadow stack. NB: This + restore token may be checked by setcontext or swapcontext + later. */ + saveprevssp + + /* Record the new shadow stack base that was switched to. */ + movq (oSSP + 8)(%rdx), %rax + movq %rax, %fs:SSP_BASE_OFFSET + +L(unwind_shadow_stack): + rdsspq %rcx + subq %rdi, %rcx + je L(skip_unwind_shadow_stack) + negq %rcx + shrq $3, %rcx + movl $255, %esi +L(loop): + cmpq %rsi, %rcx + cmovb %rcx, %rsi + incsspq %rsi + subq %rsi, %rcx + ja L(loop) + +L(skip_unwind_shadow_stack): + movq oRSI(%rdx), %rsi + movq oRDI(%rdx), %rdi + movq oRCX(%rdx), %rcx + movq oR8(%rdx), %r8 + movq oR9(%rdx), %r9 + + /* Get the return address set with getcontext. */ + movq oRIP(%rdx), %r10 + + /* Setup finally %rdx. */ + movq oRDX(%rdx), %rdx + + /* Check if return address is valid for the case when setcontext + is invoked from __start_context with linked context. */ + rdsspq %rax + cmpq (%rax), %r10 + /* Clear RAX to indicate success. NB: Don't use xorl to keep + EFLAGS for jne. */ + movl $0, %eax + jne L(jmp) + /* Return to the new context if return address valid. */ + pushq %r10 + ret + +L(jmp): + /* Jump to the new context directly. */ + jmp *%r10 + +L(no_shstk): +#endif /* The following ret should return to the address set with getcontext. Therefore push the address on the stack. */ movq oRIP(%rdx), %rcx |