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Date: Thu, 7 Jul 2016 13:29:38 -0400 From: Kees Cook <keescook@...omium.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: LKML <linux-kernel@...r.kernel.org>, Rik van Riel <riel@...hat.com>, Casey Schaufler <casey@...aufler-ca.com>, PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>, Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Michael Ellerman <mpe@...erman.id.au>, Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, "David S. Miller" <davem@...emloft.net>, "x86@...nel.org" <x86@...nel.org>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>, Mathias Krause <minipli@...glemail.com>, Jan Kara <jack@...e.cz>, Vitaly Wool <vitalywool@...il.com>, Andrea Arcangeli <aarcange@...hat.com>, Dmitry Vyukov <dvyukov@...gle.com>, Laura Abbott <labbott@...oraproject.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, linux-ia64@...r.kernel.org, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, sparclinux <sparclinux@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH 1/9] mm: Hardened usercopy On Thu, Jul 7, 2016 at 3:42 AM, Thomas Gleixner <tglx@...utronix.de> wrote: > On Wed, 6 Jul 2016, Kees Cook wrote: >> + >> +#if defined(CONFIG_FRAME_POINTER) && defined(CONFIG_X86) >> + const void *frame = NULL; >> + const void *oldframe; >> +#endif > > That's ugly Yeah, I'd like to have this be controlled by a specific CONFIG, like I invented for the linear mapping, but I wasn't sure what was the best approach. > >> + >> + /* Object is not on the stack at all. */ >> + if (obj + len <= stack || stackend <= obj) >> + return 0; >> + >> + /* >> + * Reject: object partially overlaps the stack (passing the >> + * the check above means at least one end is within the stack, >> + * so if this check fails, the other end is outside the stack). >> + */ >> + if (obj < stack || stackend < obj + len) >> + return -1; >> + >> +#if defined(CONFIG_FRAME_POINTER) && defined(CONFIG_X86) >> + oldframe = __builtin_frame_address(1); >> + if (oldframe) >> + frame = __builtin_frame_address(2); >> + /* >> + * low ----------------------------------------------> high >> + * [saved bp][saved ip][args][local vars][saved bp][saved ip] >> + * ^----------------^ >> + * allow copies only within here >> + */ >> + while (stack <= frame && frame < stackend) { >> + /* >> + * If obj + len extends past the last frame, this >> + * check won't pass and the next frame will be 0, >> + * causing us to bail out and correctly report >> + * the copy as invalid. >> + */ >> + if (obj + len <= frame) >> + return obj >= oldframe + 2 * sizeof(void *) ? 2 : -1; >> + oldframe = frame; >> + frame = *(const void * const *)frame; >> + } >> + return -1; >> +#else >> + return 1; >> +#endif > > I'd rather make that a weak function returning 1 which can be replaced by > x86 for CONFIG_FRAME_POINTER=y. That also allows other architectures to > implement their specific frame checks. Yeah, though I prefer CONFIG-controlled stuff over weak functions, but I agree, something like arch_check_stack_frame(...) or similar. I'll build something for this on the next revision. -Kees -- Kees Cook Chrome OS & Brillo Security
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