Messages in this thread | | | Date | Wed, 19 Oct 2022 14:03:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/ibt: Implement FineIBT |
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On Tue, Oct 18, 2022 at 10:05:26PM -0700, Kees Cook wrote:
> > +static int cfi_rand_preamble(s32 *start, s32 *end) > > +{ > > + s32 *s; > > + > > + for (s = start; s < end; s++) { > > + void *addr = (void *)s + *s; > > + u32 hash; > > + > > + hash = decode_preamble_hash(addr); > > + if (WARN(!hash, "no CFI hash found at: %pS %px %*ph\n", > > + addr, addr, 5, addr)) > > + return -EINVAL; > > + > > + hash ^= cfi_seed; > > + text_poke_early(addr + 1, &hash, 4); > > + } > > + > > + return 0; > > +} > > The one glitch here is that the resulting hash needs to not contain > an endbr...
Oh right,.. duh. How about something like:
static u32 cfi_rehash(u32 hash) { hash ^= cfi_hash; while (unlikely(is_endbr(hash))) { bool lsb = hash & 1; hash >>= 1; if (lsb) hash ^= 0x80200003; } return hash; }
Which seems properly over-engineered :-)
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