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| author | Peter Zijlstra <peterz@infradead.org> | 2019-02-14 10:30:52 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-04-03 09:36:27 +0200 |
| commit | 6690e86be83ac75832e461c141055b5d601c0a6d (patch) | |
| tree | ac9835c1ef68ed66a41977c0f7f9f788a0b6a6a4 /arch/x86/entry | |
| parent | 5e7a8ca319268a70a6c7c3c1fde5bea38e1e5539 (diff) | |
| download | linux-6690e86be83ac75832e461c141055b5d601c0a6d.tar.gz linux-6690e86be83ac75832e461c141055b5d601c0a6d.tar.bz2 linux-6690e86be83ac75832e461c141055b5d601c0a6d.zip | |
sched/x86: Save [ER]FLAGS on context switch
Effectively reverts commit:
2c7577a75837 ("sched/x86_64: Don't save flags on context switch")
Specifically because SMAP uses FLAGS.AC which invalidates the claim
that the kernel has clean flags.
In particular; while preemption from interrupt return is fine (the
IRET frame on the exception stack contains FLAGS) it breaks any code
that does synchonous scheduling, including preempt_enable().
This has become a significant issue ever since commit:
5b24a7a2aa20 ("Add 'unsafe' user access functions for batched accesses")
provided for means of having 'normal' C code between STAC / CLAC,
exposing the FLAGS.AC state. So far this hasn't led to trouble,
however fix it before it comes apart.
Reported-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
Fixes: 5b24a7a2aa20 ("Add 'unsafe' user access functions for batched accesses")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry')
| -rw-r--r-- | arch/x86/entry/entry_32.S | 2 | ||||
| -rw-r--r-- | arch/x86/entry/entry_64.S | 2 |
2 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index d309f30cf7af..5fc76b755510 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -650,6 +650,7 @@ ENTRY(__switch_to_asm) pushl %ebx pushl %edi pushl %esi + pushfl /* switch stack */ movl %esp, TASK_threadsp(%eax) @@ -672,6 +673,7 @@ ENTRY(__switch_to_asm) #endif /* restore callee-saved registers */ + popfl popl %esi popl %edi popl %ebx diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 1f0efdb7b629..4fe27b67d7e2 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -291,6 +291,7 @@ ENTRY(__switch_to_asm) pushq %r13 pushq %r14 pushq %r15 + pushfq /* switch stack */ movq %rsp, TASK_threadsp(%rdi) @@ -313,6 +314,7 @@ ENTRY(__switch_to_asm) #endif /* restore callee-saved registers */ + popfq popq %r15 popq %r14 popq %r13 |