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Subject[PATCH] x86/asm/entry/32: Simplify zeroing of pt_regs->r8..r11 on int80 code path
Date
32-bit syscall entry points do not save complete pt_regs struct -
they leave some fields uninitialized. However, they must be careful
to not leak uninitialized data in pt_regs->r8..r11 to ptrace users.

CLEAR_RREGS macro is used to zero these fields out when needed.

However, on int80 code path this zeroing is unconditional. This patch
simplifies it by storing zeroes there right away, when pt_regs
is constructed on stack. This uses shrter instructions:

text data bss dec hex filename
1423 0 0 1423 58f ia32entry.o.before
1407 0 0 1407 57f ia32entry.o

Compile-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---
arch/x86/ia32/ia32entry.S | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 2be23c7..2801cbe 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -421,6 +421,10 @@ ia32_badarg:
movq $-EFAULT,%rax
jmp ia32_sysret

+ia32_ret_from_sys_call:
+ CLEAR_RREGS
+ jmp int_ret_from_sys_call
+
/*
* Emulated IA32 system calls via int 0x80.
*
@@ -462,8 +466,12 @@ ENTRY(ia32_syscall)
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
+ pushq $0 /* pt_regs->r8 */
+ pushq $0 /* pt_regs->r9 */
+ pushq $0 /* pt_regs->r10 */
+ pushq $0 /* pt_regs->r11 */
cld
- sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
+ sub $(6*8),%rsp /* pt_regs->bp,bx,r12-15 not saved */

orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -481,13 +489,10 @@ ia32_do_call:
ia32_sysret:
movq %rax,RAX(%rsp)
1:
-ia32_ret_from_sys_call:
- CLEAR_RREGS
jmp int_ret_from_sys_call

ia32_tracesys:
SAVE_EXTRA_REGS
- CLEAR_RREGS
movq %rsp,%rdi /* &pt_regs -> arg1 */
call syscall_trace_enter
LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
--
1.8.1.4


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