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authorAndy Lutomirski <luto@kernel.org>2016-04-04 18:46:22 +0300
committerIngo Molnar <mingo@kernel.org>2016-04-13 12:37:47 +0300
commit60a0e2039e3df6c0a2b896bd78af36ff36fb629c (patch)
treea057af18b433a4217a0e1d43917cde8b701eecc8 /arch/x86/mm/extable.c
parentb828b79fcced0e66492590707649dbfaea6435e6 (diff)
downloadlinux-60a0e2039e3df6c0a2b896bd78af36ff36fb629c.tar.xz
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>
Diffstat (limited to 'arch/x86/mm/extable.c')
-rw-r--r--arch/x86/mm/extable.c14
1 files changed, 14 insertions, 0 deletions
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index fd9eb98c4f58..aaeda3ffaafe 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;