Commit cd88ec23 authored Aug 13, 2015 by Linus Torvalds

x86: fix error handling for 32-bit compat out-of-range system call numbers



Commit 3f5159a9 ("x86/asm/entry/32: Update -ENOSYS handling to match
the 64-bit logic") broke the ENOSYS handling for the 32-bit compat case.
The proper error return value was never loaded into %rax, except if
things just happened to go through the audit paths, which ended up
reloading the return value.

This moves the loading or %rax into the normal system call path, just to
make sure the error case triggers it.  It's kind of sad, since it adds a
useless instruction to reload the register to the fast path, but it's
not like that single load from the stack is going to be noticeable.

Reported-by: David Drysdale <drysdale@google.com>
Tested-by: Kees Cook <keescook@chromium.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5b3e2e14

arch/x86/entry/entry_64_compat.S

+2 −1

Original line number	Diff line number	Diff line
		@@ -140,6 +140,7 @@ sysexit_from_sys_call:
		*/
		andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
		movl RIP(%rsp), %ecx /* User %eip */
		movq RAX(%rsp), %rax
		RESTORE_RSI_RDI
		xorl %edx, %edx /* Do not leak kernel information */
		xorq %r8, %r8
		@@ -219,7 +220,6 @@ sysexit_from_sys_call:
		1: setbe %al /* 1 if error, 0 if not */
		movzbl %al, %edi /* zero-extend that into %edi */
		call __audit_syscall_exit
		movq RAX(%rsp), %rax /* reload syscall return value */
		movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %edi
		DISABLE_INTERRUPTS(CLBR_NONE)
		TRACE_IRQS_OFF
		@@ -368,6 +368,7 @@ sysretl_from_sys_call:
		RESTORE_RSI_RDI_RDX
		movl RIP(%rsp), %ecx
		movl EFLAGS(%rsp), %r11d
		movq RAX(%rsp), %rax
		xorq %r10, %r10
		xorq %r9, %r9
		xorq %r8, %r8