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authorPeter Zijlstra <peterz@infradead.org>2019-02-14 10:30:52 +0100
committerIngo Molnar <mingo@kernel.org>2019-04-03 09:36:27 +0200
commit6690e86be83ac75832e461c141055b5d601c0a6d (patch)
treeac9835c1ef68ed66a41977c0f7f9f788a0b6a6a4 /arch/x86/entry
parentMerge branch 'work.aio' of git://git.kernel.org/pub/scm/linux/kernel/git/viro... (diff)
downloadlinux-6690e86be83ac75832e461c141055b5d601c0a6d.tar.xz
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.S2
-rw-r--r--arch/x86/entry/entry_64.S2
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