linux-kernel - Re: Out-of-bounds access in vread

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Message-ID: <CALCETrU9QFBhJeES61FiKbNsF=ZUnmF9H3cg-6Gup-ov3PrpyA@mail.gmail.com>
Date:	Tue, 10 Jun 2014 09:13:49 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Richard Weinberger <richard@....at>
Cc:	"the arch/x86 maintainers" <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Out-of-bounds access in vread_hpet()

On Mon, Jun 9, 2014 at 11:36 PM, Richard Weinberger <richard@....at> wrote:
> FYI:
> ________________________________________________________________________________________________________
> *** CID 1222081:  Out-of-bounds access  (ARRAY_VS_SINGLETON)
> /arch/x86/vdso/vclock_gettime.c: 38 in vread_hpet()
> 32     #ifdef CONFIG_HPET_TIMER
> 33     extern u8 hpet_page
> 34      __attribute__((visibility("hidden")));
> 35
> 36     static notrace cycle_t vread_hpet(void)
> 37     {
>>>>     CID 1222081:  Out-of-bounds access  (ARRAY_VS_SINGLETON)
>>>>     Using "&hpet_page" as an array.  This might corrupt or misinterpret adjacent memory locations.
> 38      return *(const volatile u32 *)(&hpet_page + HPET_COUNTER);

That's a false positive.  HPET_COUNTER is a compile-time constant
index of a register, and hpet_page is the base address where the thing
is mapped.

I can change the code if there's something non-ugly that makes it
clearer, but ISTM that this particular warning might not make so much
sense when the offset is a real constant like this.

Hmm.  Maybe hpet_page could be redefined as const char hpet_page[PAGE_SIZE].

--Andy
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