Messages in this thread Patch in this message | | | Date | Wed, 13 Apr 2016 04:46:52 -0700 | From | tip-bot for Andy Lutomirski <> | Subject | [tip:x86/asm] x86/extable: Add a comment about early exception handlers |
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Commit-ID: 60a0e2039e3df6c0a2b896bd78af36ff36fb629c Gitweb: http://git.kernel.org/tip/60a0e2039e3df6c0a2b896bd78af36ff36fb629c Author: Andy Lutomirski <luto@kernel.org> AuthorDate: Mon, 4 Apr 2016 08:46:22 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 13 Apr 2016 11:37:47 +0200
x86/extable: Add a comment about early exception handlers
Borislav asked for a comment explaining why all exception handlers are allowed early.
Signed-off-by: Andy Lutomirski <luto@kernel.org> Reviewed-by: Borislav Petkov <bp@suse.de> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: KVM list <kvm@vger.kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: xen-devel <Xen-devel@lists.xen.org> Link: http://lkml.kernel.org/r/5f1dcd6919f4a5923959a8065cb2c04d9dac1412.1459784772.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/mm/extable.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index fd9eb98..aaeda3f 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -125,6 +125,20 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr) if (regs->cs != __KERNEL_CS) goto fail; + /* + * The full exception fixup machinery is available as soon as + * the early IDT is loaded. This means that it is the + * responsibility of extable users to either function correctly + * when handlers are invoked early or to simply avoid causing + * exceptions before they're ready to handle them. + * + * This is better than filtering which handlers can be used, + * because refusing to call a handler here is guaranteed to + * result in a hard-to-debug panic. + * + * Keep in mind that not all vectors actually get here. Early + * fage faults, for example, are special. + */ if (fixup_exception(regs, trapnr)) return;
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