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Date: Mon, 14 Apr 2014 23:31:51 -0700 From: Alexei Starovoitov <ast@...mgrid.com> To: Andy Lutomirski <luto@...capital.net> Cc: David Miller <davem@...emloft.net>, Daniel Borkmann <dborkman@...hat.com>, Network Development <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Eric Paris <eparis@...hat.com>, James Morris <james.l.morris@...cle.com>, Kees Cook <keescook@...omium.org> Subject: Re: [PATCH] seccomp: fix populating a0-a5 syscall args in 32-bit x86 BPF On Mon, Apr 14, 2014 at 1:28 PM, Andy Lutomirski <luto@...capital.net> wrote: > On Mon, Apr 14, 2014 at 1:24 PM, David Miller <davem@...emloft.net> wrote: >> From: Andy Lutomirski <luto@...capital.net> >> Date: Mon, 14 Apr 2014 13:13:45 -0700 >> >>> I think this description is wrong. (unsigned long *) &sd->args[1] is >>> the right location, at least on 32-bit little-endian architectures. >> >> It absolutely is not. > > Huh? It's a pointer to the right address, but the type is wrong. > > The changelog says "on 32-bit x86 (or any other 32bit arch), it would > result in storing a0-a5 at wrong offsets in args[] member". Unless > I'm mistaken, this is incorrect: a0-a5 are are the correct offsets, > but they are stored with the wrong type, so the other bits in there > are garbage. agree. your above description is more correct than the log. We were focusing on the bug itself and the log came a bit misleading as a result of multiple iterations back and forth between me and Daniel. also the log says: "gcc is clever and optimizes the copy away in other cases, e.g. x86_64" since we actually checked assembler, so the fix doesn't pessimize 64-bit architectures :) This function is in critical path for seccomp, so performance definitely matters. >> >> The thing is a u64, and we must respect that type in a completely >> portable way. >> >> Daniel's change is %100 correct, portable, and doesn't have any >> ugly ifdef crap. >> > > I have no problem with the patch itself. I'm suggesting that a better > changelog message would confuse other people reading the same patch > less. > > --Andy -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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