Commit 33db1fd4 authored Mar 17, 2015 by Denys Vlasenko Committed by Ingo Molnar Mar 17, 2015

x86/asm/entry/64: Enable interrupts after we fetch PER_CPU_VAR(old_rsp)



We want to use PER_CPU_VAR(old_rsp) as a simple temporary register,
to shuffle user-space RSP into (and from) when we set up the system
call stack frame. At that point we cannot shuffle values into general
purpose registers, because we have not saved them yet.

To be able to do this shuffling into a memory location, we must be
atomic and must not be preempted while we do the shuffling, otherwise
the 'temporary' register gets overwritten by some other task's
temporary register contents ...

Tested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1426600344-8254-1-git-send-email-dvlasenk@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8b6c0ab1

arch/x86/kernel/entry_64.S

+5 −5

Original line number	Original line	Diff line number	Diff line
	@@ -241,16 +241,16 @@ GLOBAL(system_call_after_swapgs)
	movq %rsp,PER_CPU_VAR(old_rsp)		movq %rsp,PER_CPU_VAR(old_rsp)
	/* kernel_stack is set so that 5 slots (iret frame) are preallocated */		/* kernel_stack is set so that 5 slots (iret frame) are preallocated */
	movq PER_CPU_VAR(kernel_stack),%rsp		movq PER_CPU_VAR(kernel_stack),%rsp
	/*
	* No need to follow this irqs off/on section - it's straight
	* and short:
	*/
	ENABLE_INTERRUPTS(CLBR_NONE)
	ALLOC_PT_GPREGS_ON_STACK 8 /* +8: space for orig_ax */		ALLOC_PT_GPREGS_ON_STACK 8 /* +8: space for orig_ax */
	movq %rcx,RIP(%rsp)		movq %rcx,RIP(%rsp)
	movq PER_CPU_VAR(old_rsp),%rcx		movq PER_CPU_VAR(old_rsp),%rcx
	movq %r11,EFLAGS(%rsp)		movq %r11,EFLAGS(%rsp)
	movq %rcx,RSP(%rsp)		movq %rcx,RSP(%rsp)
			/*
			* No need to follow this irqs off/on section - it's straight
			* and short:
			*/
			ENABLE_INTERRUPTS(CLBR_NONE)
	movq_cfi rax,ORIG_RAX		movq_cfi rax,ORIG_RAX
	SAVE_C_REGS_EXCEPT_RAX_RCX_R11		SAVE_C_REGS_EXCEPT_RAX_RCX_R11
	movq $-ENOSYS,RAX(%rsp)		movq $-ENOSYS,RAX(%rsp)