* [PATCH] x86/extable: Add a comment about early exception handlers
@ 2016-04-04 15:46 Andy Lutomirski
0 siblings, 0 replies; 2+ messages in thread
From: Andy Lutomirski @ 2016-04-04 15:46 UTC (permalink / raw)
To: X86 ML
Cc: KVM list, Peter Zijlstra, Linus Torvalds, linux-kernel,
xen-devel, Borislav Petkov, Andy Lutomirski, Paolo Bonzini,
Andrew Morton, Arjan van de Ven
Borislav asked for a comment explaining why all exception handlers are
allowed early.
Signed-off-by: Andy Lutomirski <luto@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 98b5f45d9d79..36fe03bc81ee 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -132,6 +132,20 @@ 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;
--
2.5.5
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^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] x86/extable: Add a comment about early exception handlers
[not found] <5f1dcd6919f4a5923959a8065cb2c04d9dac1412.1459784772.git.luto@kernel.org>
@ 2016-04-04 16:16 ` Borislav Petkov
0 siblings, 0 replies; 2+ messages in thread
From: Borislav Petkov @ 2016-04-04 16:16 UTC (permalink / raw)
To: Andy Lutomirski
Cc: KVM list, Peter Zijlstra, Linus Torvalds, X86 ML, linux-kernel,
xen-devel, Paolo Bonzini, Andrew Morton, Arjan van de Ven
On Mon, Apr 04, 2016 at 08:46:22AM -0700, Andy Lutomirski wrote:
> Borislav asked for a comment explaining why all exception handlers are
> allowed early.
>
> Signed-off-by: Andy Lutomirski <luto@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 98b5f45d9d79..36fe03bc81ee 100644
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -132,6 +132,20 @@ 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;
>
> --
Thanks!
Reviewed-by: Borislav Petkov <bp@suse.de>
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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2016-04-04 15:46 [PATCH] x86/extable: Add a comment about early exception handlers Andy Lutomirski
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2016-04-04 16:16 ` Borislav Petkov
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