[PATCH v3] powerpc/64: Fix memcmp reading past the end of src/dest
segher at kernel.crashing.org
Sat Mar 23 05:29:43 AEDT 2019
On Fri, Mar 22, 2019 at 11:37:24PM +1100, Michael Ellerman wrote:
> - /* Here we have only less than 8 bytes to compare with. at least s1
> - * Address is aligned with 8 bytes.
> - * The next double words are load and shift right with appropriate
> - * bits.
> + /*
> + * Here we have less than 8 bytes to compare. At least s1 is aligned to
> + * 8 bytes, but s2 may not be. We must make sure s2 + 8 doesn't cross a
"s2 + 7"? The code is fine though (bgt, not bge).
> + * page boundary, otherwise we might read past the end of the buffer and
> + * trigger a page fault. We use 4K as the conservative minimum page
> + * size. If we detect that case we go to the byte-by-byte loop.
> + *
> + * Otherwise the next double word is loaded from s1 and s2, and shifted
> + * right to compare the appropriate bits.
> + clrldi r6,r4,(64-12) // r6 = r4 & 0xfff
You can just write
if that is clearer? Or do you still want a comment with that :-)
> + cmpdi r6,0xff8
> + bgt .Lshort
Reviewed-by: Segher Boessenkool <segher at kernel.crashing.org>
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