* Andrey Konovalov <[email protected]> wrote:
> On Sat, Mar 24, 2018 at 9:29 AM, Ingo Molnar <[email protected]> wrote:
> >
> > * Andrey Konovalov <[email protected]> wrote:
> >
> >> The krealloc function checks where the same buffer was reused or a new one
> >> allocated by comparing kernel pointers. KHWASAN changes memory tag on the
> >> krealloc'ed chunk of memory and therefore also changes the pointer tag of
> >> the returned pointer. Therefore we need to perform comparison on untagged
> >> (with tags reset) pointers to check whether it's the same memory region or
> >> not.
> >>
> >> Signed-off-by: Andrey Konovalov <[email protected]>
> >> ---
> >> mm/slab_common.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/mm/slab_common.c b/mm/slab_common.c
> >> index a33e61315ca6..5911f2194cf7 100644
> >> --- a/mm/slab_common.c
> >> +++ b/mm/slab_common.c
> >> @@ -1494,7 +1494,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t
> >> flags)
> >> }
> >>
> >> ret = __do_krealloc(p, new_size, flags);
> >> - if (ret && p != ret)
> >> + if (ret && khwasan_reset_tag(p) != khwasan_reset_tag(ret))
> >> kfree(p);
> >
> > Small nit:
> >
> > If 'reset' here means an all zeroes tag (upper byte) then
> > khwasan_clear_tag()
> > might be a slightly easier to read primitive?
>
> 'Reset' means to set the upper byte to the value that is native for
> kernel pointers, and that is 0xFF. So it sets the tag to all ones, not
> all zeroes. I can still rename it to khwasan_clear_tag(), if you think
> that makes sense in this case as well.
Ok, if it's not 0 then I agree that 'reset' is the better name. 'clear' would
in
fact be actively confusing.
Thanks,
Ingo
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