On Mon, Aug 7, 2017 at 2:27 PM, Ard Biesheuvel <[email protected]> wrote: > On 7 August 2017 at 21:39, Kees Cook <[email protected]> wrote: >> Two new tests STACK_GUARD_PAGE_LEADING and STACK_GUARD_PAGE_TRAILING >> attempt to read the byte before and after, respectively, of the current >> stack frame, which should fault under VMAP_STACK. >> >> Signed-off-by: Kees Cook <[email protected]> >> --- >> Do these tests both trip with the new arm64 VMAP_STACK code? > > Probably not. On arm64, the registers are stacked by software at > exception entry, and so we decrement the sp first by the size of the > register file, and if the resulting value overflows the stack, the > situation is handled as if the exception was caused by a faulting > stack access while it may be caused by something else in reality. > Since the act of handling the exception is guaranteed to overflow the > stack anyway, this does not really make a huge difference, and it > prevents the recursive fault from wiping the context that we need to > produce the diagnostics. > > This means an illegal access right above the stack will go undetected.
I thought vmap entries provided guard pages around allocations? Shouldn't that catch it? -- Kees Cook Pixel Security
