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x86/entry: Use PUSH_AND_CLEAR_REGS for compat

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Since the upper regs don't exist for ia32 code, preserving them
doesn't hurt and it simplifies the code.

This doesn't add any attack surface that would not already be
available through INT80.

Notably:

 - 32bit SYSENTER: didn't clear si, dx, cx.

 - 32bit SYSCALL, INT80: *do* clear si since the C functions don't
   take a second argument.

 - 64bit: didn't clear si since the C functions take a second
   argument; except the error_entry path might have only one argument,
   so clearing si was missing here.

32b SYSENTER should be clearing all those 3 registers, nothing uses them
and selftests pass.

Unconditionally clear rsi since it simplifies code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220506121631.293889636@infradead.org
This commit is contained in:
Peter Zijlstra 2022-05-06 14:14:34 +02:00 committed by Borislav Petkov
parent d205222eb6
commit 8c42819b61
2 changed files with 4 additions and 84 deletions
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1
arch/x86/entry/calling.h
View File

@ -99,6 +99,7 @@ For 32-bit we have the following conventions - kernel is built with
* well before they could be put to use in a speculative execution
* gadget.
*/
xorl %esi, %esi /* nospec si */
xorl %edx, %edx /* nospec dx */
xorl %ecx, %ecx /* nospec cx */
xorl %r8d, %r8d /* nospec r8 */

87
arch/x86/entry/entry_64_compat.S
View File

@ -83,32 +83,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
movl %eax, %eax
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
pushq $0 /* pt_regs->r8 = 0 */
xorl %r8d, %r8d /* nospec r8 */
pushq $0 /* pt_regs->r9 = 0 */
xorl %r9d, %r9d /* nospec r9 */
pushq $0 /* pt_regs->r10 = 0 */
xorl %r10d, %r10d /* nospec r10 */
pushq $0 /* pt_regs->r11 = 0 */
xorl %r11d, %r11d /* nospec r11 */
pushq %rbx /* pt_regs->rbx */
xorl %ebx, %ebx /* nospec rbx */
pushq %rbp /* pt_regs->rbp (will be overwritten) */
xorl %ebp, %ebp /* nospec rbp */
pushq $0 /* pt_regs->r12 = 0 */
xorl %r12d, %r12d /* nospec r12 */
pushq $0 /* pt_regs->r13 = 0 */
xorl %r13d, %r13d /* nospec r13 */
pushq $0 /* pt_regs->r14 = 0 */
xorl %r14d, %r14d /* nospec r14 */
pushq $0 /* pt_regs->r15 = 0 */
xorl %r15d, %r15d /* nospec r15 */
PUSH_AND_CLEAR_REGS rax=$-ENOSYS
UNWIND_HINT_REGS
cld
@ -225,35 +200,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
movl %eax, %eax /* discard orig_ax high bits */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
xorl %esi, %esi /* nospec si */
pushq %rdx /* pt_regs->dx */
xorl %edx, %edx /* nospec dx */
pushq %rbp /* pt_regs->cx (stashed in bp) */
xorl %ecx, %ecx /* nospec cx */
pushq $-ENOSYS /* pt_regs->ax */
pushq $0 /* pt_regs->r8 = 0 */
xorl %r8d, %r8d /* nospec r8 */
pushq $0 /* pt_regs->r9 = 0 */
xorl %r9d, %r9d /* nospec r9 */
pushq $0 /* pt_regs->r10 = 0 */
xorl %r10d, %r10d /* nospec r10 */
pushq $0 /* pt_regs->r11 = 0 */
xorl %r11d, %r11d /* nospec r11 */
pushq %rbx /* pt_regs->rbx */
xorl %ebx, %ebx /* nospec rbx */
pushq %rbp /* pt_regs->rbp (will be overwritten) */
xorl %ebp, %ebp /* nospec rbp */
pushq $0 /* pt_regs->r12 = 0 */
xorl %r12d, %r12d /* nospec r12 */
pushq $0 /* pt_regs->r13 = 0 */
xorl %r13d, %r13d /* nospec r13 */
pushq $0 /* pt_regs->r14 = 0 */
xorl %r14d, %r14d /* nospec r14 */
pushq $0 /* pt_regs->r15 = 0 */
xorl %r15d, %r15d /* nospec r15 */
PUSH_AND_CLEAR_REGS rax=$-ENOSYS
UNWIND_HINT_REGS
movq %rsp, %rdi
@ -380,35 +327,7 @@ SYM_CODE_START(entry_INT80_compat)
pushq 0*8(%rax) /* regs->orig_ax */
.Lint80_keep_stack:
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
xorl %esi, %esi /* nospec si */
pushq %rdx /* pt_regs->dx */
xorl %edx, %edx /* nospec dx */
pushq %rcx /* pt_regs->cx */
xorl %ecx, %ecx /* nospec cx */
pushq $-ENOSYS /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 */
xorl %r8d, %r8d /* nospec r8 */
pushq %r9 /* pt_regs->r9 */
xorl %r9d, %r9d /* nospec r9 */
pushq %r10 /* pt_regs->r10*/
xorl %r10d, %r10d /* nospec r10 */
pushq %r11 /* pt_regs->r11 */
xorl %r11d, %r11d /* nospec r11 */
pushq %rbx /* pt_regs->rbx */
xorl %ebx, %ebx /* nospec rbx */
pushq %rbp /* pt_regs->rbp */
xorl %ebp, %ebp /* nospec rbp */
pushq %r12 /* pt_regs->r12 */
xorl %r12d, %r12d /* nospec r12 */
pushq %r13 /* pt_regs->r13 */
xorl %r13d, %r13d /* nospec r13 */
pushq %r14 /* pt_regs->r14 */
xorl %r14d, %r14d /* nospec r14 */
pushq %r15 /* pt_regs->r15 */
xorl %r15d, %r15d /* nospec r15 */
PUSH_AND_CLEAR_REGS rax=$-ENOSYS
UNWIND_HINT_REGS
cld