Messages in this thread | | | Date | Wed, 16 Aug 2023 11:39:55 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/static_call: Fix __static_call_fixup() |
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On Tue, Aug 15, 2023 at 08:41:12PM -0400, Steven Rostedt wrote: > On Wed, 16 Aug 2023 01:08:09 +0200 > Peter Zijlstra <peterz@infradead.org> wrote: > > > > diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c > > index b70670a98597..2e67512d7104 100644 > > --- a/arch/x86/kernel/static_call.c > > +++ b/arch/x86/kernel/static_call.c > > @@ -186,6 +186,16 @@ EXPORT_SYMBOL_GPL(arch_static_call_transform); > > */ > > bool __static_call_fixup(void *tramp, u8 op, void *dest) > > { > > + /* > > + * Not all .return_sites are a static_call trampoline (most are not). > > + * Check if the next 3 bytes are still kernel text, if not, then this > > + * definitely is not a trampoline and we need not worry further. > > + * > > + * This avoids the memcmp() below tripping over pagefaults etc.. > > + */ > > + if (!kernel_text_address(tramp+7)) > > The comment says "next 3 bytes" and the test is "tramp+7". Why the magic 7 number? > > If the tramp is 5 bytes, shouldn't it be +8?
0 based, 7 is the last of the 8 bytes. +8 would be one beyond.
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