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Date: Tue, 18 Jan 2022 15:39:31 -0400 From: Jason Gunthorpe <jgg@...pe.ca> To: Jann Horn <jannh@...gle.com> Cc: Kees Cook <keescook@...omium.org>, Peter Huewe <peterhuewe@....de>, Jarkko Sakkinen <jarkko@...nel.org>, linux-integrity@...r.kernel.org, Stefan Berger <stefanb@...ux.ibm.com>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH v2] tpm: vtpm_proxy: Double-check to avoid buffer overflow On Tue, Jan 18, 2022 at 08:32:43PM +0100, Jann Horn wrote: > On Tue, Jan 18, 2022 at 7:37 PM Kees Cook <keescook@...omium.org> wrote: > > When building with -Warray-bounds, this warning was emitted: > > > > In function 'memset', > > inlined from 'vtpm_proxy_fops_read' at drivers/char/tpm/tpm_vtpm_proxy.c:102:2: > > ./include/linux/fortify-string.h:43:33: warning: '__builtin_memset' pointer overflow between offset 164 and size [2147483648, 4294967295] > > [-Warray-bounds] > > 43 | #define __underlying_memset __builtin_memset > > | ^ > > Can you explain what that compiler warning actually means, and which > compiler it is from? Is this from a 32-bit or a 64-bit architecture? > > It sounds like the compiler (GCC?) is hallucinating a codepath on > which "len" is guaranteed to be >=2147483648, right? Why is it doing > that? Is this some kinda side effect from the fortify code? I agree, this looks bogus, or at least the commit message neeeds alot more explaining. static int vtpm_proxy_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t count) if (count > sizeof(proxy_dev->buffer)) [...] proxy_dev->req_len = count; Not clear how req_len can be larger than sizeof(buffer)? Jason
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