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Date: Fri, 06 May 2022 14:14:34 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
jpoimboe@...hat.com, brgerst@...il.com, jiangshanlai@...il.com,
Andrew.Cooper3@...rix.com, mark.rutland@....com,
Borislav Petkov <bp@...e.de>
Subject: [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat
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@...radead.org>
Reviewed-by: Borislav Petkov <bp@...e.de>
---
arch/x86/entry/calling.h | 1
arch/x86/entry/entry_64_compat.S | 87 +--------------------------------------
2 files changed, 4 insertions(+), 84 deletions(-)
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -99,6 +99,7 @@ For 32-bit we have the following convent
* 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 */
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -83,32 +83,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_af
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_saf
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
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