Out-of-bounds access in vread_hpet()

Out-of-bounds access in vread_hpet()

[Richard Weinberger]

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);
39     }
40     #endif
41
42     #ifndef BUILD_VDSO32
43

Thanks,
//richard

Re: Out-of-bounds access in vread_hpet()

[Andy Lutomirski]

On Mon, Jun 9, 2014 at 11:36 PM, Richard Weinberger <richard@nod.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