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syscalls/x86: Extend register clearing on syscall entry to lower registers 

To reduce the chance that random user space content leaks down the call
chain in registers, also clear lower registers on syscall entry:

For 64-bit syscalls, extend the register clearing in PUSH_AND_CLEAR_REGS
to %dx and %cx. This should not hurt at all, also on the other callers
of that macro. We do not need to clear %rdi and %rsi for syscall entry,
as those registers are used to pass the parameters to do_syscall_64().

For the 32-bit compat syscalls, do_int80_syscall_32() and
do_fast_syscall_32() each only take one parameter. Therefore, extend the
register clearing to %dx, %cx, and %si in entry_SYSCALL_compat and
entry_INT80_compat.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180405095307.3730-8-linux@dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dominik Brodowski 2018-04-05 11:53:06 +02:00 committed by Ingo Molnar
parent f8781c4a22
commit 6dc936f175
2 changed files with 8 additions and 0 deletions
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2
arch/x86/entry/calling.h
View File

@ -114,7 +114,9 @@ For 32-bit we have the following conventions - kernel is built with
pushq %rsi /* pt_regs->si */
.endif
pushq \rdx /* pt_regs->dx */
xorl %edx, %edx /* nospec dx */
pushq %rcx /* pt_regs->cx */
xorl %ecx, %ecx /* nospec cx */
pushq \rax /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 */
xorl %r8d, %r8d /* nospec r8 */

6
arch/x86/entry/entry_64_compat.S
View File

@ -220,8 +220,11 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
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 */
@ -365,8 +368,11 @@ ENTRY(entry_INT80_compat)
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 $0 /* pt_regs->r8 = 0 */
xorl %r8d, %r8d /* nospec r8 */