From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E3FEF143C4B for ; Mon, 5 Aug 2024 21:05:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722891908; cv=none; b=U7QtlXskWDPt0WnVIuKSadj0zuhSvLNnAStAKeXZocvJCZZl7ia5grMK86r5UgrsGN/pqg6or78VEbWuMLBHvOzIvUaJjPJUSVeUNQw4hoZTyd2cq9/PvsTN57Zww9KrUy9Ymz5Ckk1WcYJqlvxKNSE2/Mb6jHVJs794b9Dk1Ms= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722891908; c=relaxed/simple; bh=hNEorLFNFU6XziMXB83XWj4mCvVyNc1nseFYZY1J8Gc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=p69FAxPxpfD6DxzmlUBpvyfmg2t+OzrDOfhIjEW3PmmYFd0WIXVzZs86h0QEhzcYXWSqTcz3FB/hPUsgs7mIEiN1BZT+5YHsZZd34BP8GGbDfOYjnpX7qq9uTGWSvABD/vB8gjlmRJaKI5bMO90m+8NsLmcZMkLzM/Szhp0oHJs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Auhdec/w; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Auhdec/w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A383C4AF0E; Mon, 5 Aug 2024 21:05:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722891907; bh=hNEorLFNFU6XziMXB83XWj4mCvVyNc1nseFYZY1J8Gc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Auhdec/wyq7LGcHWI7/O+VlKCfOppR2w2Z9hc+ucl5PqwwqUaUSNi7PLygqIXCQ1u 2P+VPexYHtAa1nq3Zkau7gf2aGnvk4x8HcKAaUUHeckM7UjLs0oFfcYITYaArVniLd RgoJ7jaXWTtejKbmGVdUuXlmjY8EGpA2ceV1illlFx7F1a8KWrXqMovJgmCfwFmzpd gRIKPtJWMdAR33X4pZaPfTJvg2WHSym7hMf18RSDEfGpT56JNa9f8nrBpryXVhAQ+E xKIQgtqW5iZs8zDWw/YEUDCWp0A47MNMrcDnly0kIUy9RvgIurISzrR4m7nI8cdCQY HZBx30DXnxAJA== Date: Mon, 5 Aug 2024 14:05:06 -0700 From: Kees Cook To: jeffxu@chromium.org Cc: akpm@linux-foundation.org, jannh@google.com, sroettger@google.com, adhemerval.zanella@linaro.org, ojeda@kernel.org, adobriyan@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jorgelo@chromium.org Subject: Re: [RFC PATCH v1 1/1] binfmt_elf: mseal address zero Message-ID: <202408051402.9C0FA18A12@keescook> References: <20240801170838.356177-1-jeffxu@google.com> <20240801170838.356177-2-jeffxu@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240801170838.356177-2-jeffxu@google.com> On Thu, Aug 01, 2024 at 05:08:33PM +0000, jeffxu@chromium.org wrote: > From: Jeff Xu > > Some legacy SVr4 apps might depend on page on address zero > to be readable, however I can't find a reason that the page > ever becomes writeable, so seal it. > > If there is a compain, we can make this configurable. > > Signed-off-by: Jeff Xu > --- > fs/binfmt_elf.c | 4 ++++ > include/linux/mm.h | 4 ++++ > mm/mseal.c | 2 +- > 3 files changed, 9 insertions(+), 1 deletion(-) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 19fa49cd9907..e4d35d6f5d65 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1314,6 +1314,10 @@ static int load_elf_binary(struct linux_binprm *bprm) > emulate the SVr4 behavior. Sigh. */ > error = vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_EXEC, > MAP_FIXED | MAP_PRIVATE, 0); > + > +#ifdef CONFIG_64BIT > + do_mseal(0, PAGE_SIZE, 0); > +#endif Instead of wrapping this in #ifdefs, does it make more sense to adjust the mm.h declaration instead, like this below... > } > > regs = current_pt_regs(); > diff --git a/include/linux/mm.h b/include/linux/mm.h > index c4b238a20b76..b5fed60ddcd9 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4201,4 +4201,8 @@ void vma_pgtable_walk_end(struct vm_area_struct *vma); > > int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size); > > +#ifdef CONFIG_64BIT > +int do_mseal(unsigned long start, size_t len_in, unsigned long flags); #else static inline int do_mseal(unsigned long start, size_t len_in, unsigned long flags) { return -ENOTSUPP; } > +#endif > + > #endif /* _LINUX_MM_H */ > diff --git a/mm/mseal.c b/mm/mseal.c > index bf783bba8ed0..7a40a84569c8 100644 > --- a/mm/mseal.c > +++ b/mm/mseal.c > @@ -248,7 +248,7 @@ static int apply_mm_seal(unsigned long start, unsigned long end) > * > * unseal() is not supported. > */ > -static int do_mseal(unsigned long start, size_t len_in, unsigned long flags) > +int do_mseal(unsigned long start, size_t len_in, unsigned long flags) > { > size_t len; > int ret = 0; > -- > 2.46.0.rc1.232.g9752f9e123-goog > And if it returns an error code, should we check it when used in load_elf_binary()? (And if so, should the mm.h return 0 for non-64bit?) -- Kees Cook