From: Lasse Collin <lasse.collin@tukaani.org> To: Kees Cook <keescook@chromium.org> Cc: Ingo Molnar <mingo@kernel.org>, Baoquan He <bhe@redhat.com>, Yinghai Lu <yinghai@kernel.org>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Matt Redfearn <matt.redfearn@imgtec.com>, x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Vivek Goyal <vgoyal@redhat.com>, Andy Lutomirski <luto@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Dave Young <dyoung@redhat.com>, kernel-hardening@lists.openwall.com, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH v5 06/21] x86, KASLR: Update description for decompressor worst case size Date: Fri, 15 Apr 2016 19:17:03 +0300 [thread overview] Message-ID: <20160415191703.7a3212de@tukaani.org> (raw) In-Reply-To: <1460672954-32567-7-git-send-email-keescook@chromium.org> On 2016-04-14 Kees Cook wrote: > + * Above analysis is for decompressing gzip compressed kernel only. Up to > + * now 6 different decompressor are supported all together. There are six decompressors in Linux now, but the number can change and the comment become outdated, so I suggest omitting the exact number here. > And among them > + * xz stores data in chunks and has maximum chunk of 64K. Hence safety > + * margin should be updated to cover all decompressors so that we don't > + * need to deal with each of them separately. Please check > + * the description in lib/decompressor_xxx.c for specific information. > + * > + * extra_bytes = (uncompressed_size >> 12) + 65536 + 128. lib/decompress_xxx.c, not lib/decompressor_xxx.c. Referring to those files is problematic because only decompress_unxz.c talks about the safety margin. The explanation of the safety margin for gzip is still in misc.c instead of decompress_inflate.c. I suspect that safety margin calculations haven't been made for other compressors in Linux, so there is nothing that people could read for more information. At least such information isn't present in the comments or commit messages. For example (and a bit off-topic), there is a possible sign of too small safety margin in decompress_unlzo.c, where a memcpy call can get overlapping dest and src buffers: /* When the input data is not compressed at all, * lzo1x_decompress_safe will fail, so call memcpy() * instead */ if (unlikely(dst_len == src_len)) memcpy(out_buf, in_buf, src_len); The overlap can only happen if there's enough incompressible data near the end of the kernel image. It still works in practice as long as memcpy works with overlapping buffers for dest < src. -- Lasse Collin | IRC: Larhzu @ IRCnet & Freenode
WARNING: multiple messages have this Message-ID (diff)
From: Lasse Collin <lasse.collin@tukaani.org> To: Kees Cook <keescook@chromium.org> Cc: Ingo Molnar <mingo@kernel.org>, Baoquan He <bhe@redhat.com>, Yinghai Lu <yinghai@kernel.org>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Matt Redfearn <matt.redfearn@imgtec.com>, x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Vivek Goyal <vgoyal@redhat.com>, Andy Lutomirski <luto@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Dave Young <dyoung@redhat.com>, kernel-hardening@lists.openwall.com, LKML <linux-kernel@vger.kernel.org> Subject: [kernel-hardening] Re: [PATCH v5 06/21] x86, KASLR: Update description for decompressor worst case size Date: Fri, 15 Apr 2016 19:17:03 +0300 [thread overview] Message-ID: <20160415191703.7a3212de@tukaani.org> (raw) In-Reply-To: <1460672954-32567-7-git-send-email-keescook@chromium.org> On 2016-04-14 Kees Cook wrote: > + * Above analysis is for decompressing gzip compressed kernel only. Up to > + * now 6 different decompressor are supported all together. There are six decompressors in Linux now, but the number can change and the comment become outdated, so I suggest omitting the exact number here. > And among them > + * xz stores data in chunks and has maximum chunk of 64K. Hence safety > + * margin should be updated to cover all decompressors so that we don't > + * need to deal with each of them separately. Please check > + * the description in lib/decompressor_xxx.c for specific information. > + * > + * extra_bytes = (uncompressed_size >> 12) + 65536 + 128. lib/decompress_xxx.c, not lib/decompressor_xxx.c. Referring to those files is problematic because only decompress_unxz.c talks about the safety margin. The explanation of the safety margin for gzip is still in misc.c instead of decompress_inflate.c. I suspect that safety margin calculations haven't been made for other compressors in Linux, so there is nothing that people could read for more information. At least such information isn't present in the comments or commit messages. For example (and a bit off-topic), there is a possible sign of too small safety margin in decompress_unlzo.c, where a memcpy call can get overlapping dest and src buffers: /* When the input data is not compressed at all, * lzo1x_decompress_safe will fail, so call memcpy() * instead */ if (unlikely(dst_len == src_len)) memcpy(out_buf, in_buf, src_len); The overlap can only happen if there's enough incompressible data near the end of the kernel image. It still works in practice as long as memcpy works with overlapping buffers for dest < src. -- Lasse Collin | IRC: Larhzu @ IRCnet & Freenode
next prev parent reply other threads:[~2016-04-15 16:17 UTC|newest] Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-04-14 22:28 [PATCH v5 00/21] x86, boot: KASLR cleanup and 64-bit improvements Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-14 22:28 ` [PATCH v5 01/21] x86, KASLR: Remove unneeded boot_params argument Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-15 7:29 ` Ingo Molnar 2016-04-15 7:29 ` [kernel-hardening] " Ingo Molnar 2016-04-15 18:55 ` Kees Cook 2016-04-15 18:55 ` [kernel-hardening] " Kees Cook 2016-04-14 22:28 ` [PATCH v5 02/21] x86, KASLR: Handle kernel relocation above 2G Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-15 7:47 ` Ingo Molnar 2016-04-15 7:47 ` [kernel-hardening] " Ingo Molnar 2016-04-15 19:01 ` Kees Cook 2016-04-15 19:01 ` [kernel-hardening] " Kees Cook 2016-04-14 22:28 ` [PATCH v5 03/21] x86, KASLR: Drop CONFIG_RANDOMIZE_BASE_MAX_OFFSET Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-15 8:07 ` Ingo Molnar 2016-04-15 8:07 ` [kernel-hardening] " Ingo Molnar 2016-04-15 19:12 ` Kees Cook 2016-04-15 19:12 ` [kernel-hardening] " Kees Cook 2016-04-16 8:42 ` Ingo Molnar 2016-04-16 8:42 ` [kernel-hardening] " Ingo Molnar 2016-04-14 22:28 ` [PATCH v5 04/21] x86, boot: Move compressed kernel to end of decompression buffer Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-15 8:09 ` Ingo Molnar 2016-04-15 8:09 ` [kernel-hardening] " Ingo Molnar 2016-04-18 16:50 ` Kees Cook 2016-04-18 16:50 ` [kernel-hardening] " Kees Cook 2016-04-15 9:05 ` Ingo Molnar 2016-04-15 9:05 ` [kernel-hardening] " Ingo Molnar 2016-04-14 22:28 ` [PATCH v5 05/21] x86, boot: Calculate decompression size during boot not build Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-15 8:12 ` Ingo Molnar 2016-04-15 8:12 ` [kernel-hardening] " Ingo Molnar 2016-04-15 19:14 ` Kees Cook 2016-04-15 19:14 ` [kernel-hardening] " Kees Cook 2016-04-14 22:28 ` [PATCH v5 06/21] x86, KASLR: Update description for decompressor worst case size Kees Cook 2016-04-14 22:28 ` [kernel-hardening] " Kees Cook 2016-04-15 16:17 ` Lasse Collin [this message] 2016-04-15 16:17 ` [kernel-hardening] " Lasse Collin 2016-04-14 22:29 ` [PATCH v5 07/21] x86, boot: Fix run_size calculation Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-15 8:31 ` Ingo Molnar 2016-04-15 8:31 ` [kernel-hardening] " Ingo Molnar 2016-04-15 19:26 ` Kees Cook 2016-04-15 19:26 ` [kernel-hardening] " Kees Cook 2016-04-16 9:00 ` Ingo Molnar 2016-04-16 9:00 ` [kernel-hardening] " Ingo Molnar 2016-04-14 22:29 ` [PATCH v5 08/21] x86, KASLR: Clean up unused code from old run_size Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 09/21] x86, KASLR: Correctly bounds-check relocations Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 10/21] x86, KASLR: Consolidate mem_avoid entries Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 11/21] x86, boot: Split out kernel_ident_mapping_init Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 12/21] x86, 64bit: Set ident_mapping for KASLR Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 13/21] x86, boot: Report overlap failures in memcpy Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-15 14:42 ` Lasse Collin 2016-04-15 14:42 ` [kernel-hardening] " Lasse Collin 2016-04-15 19:28 ` Kees Cook 2016-04-15 19:28 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 14/21] x86, KASLR: Add slot_area to manage random slots Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 15/21] x86, KASLR: Add slot_area support functions Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 16/21] x86, KASLR: Add virtual address choosing function Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 17/21] x86, KASLR: Clarify purpose of each get_random_long Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 18/21] x86, KASLR: Randomize virtual address separately Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 19/21] x86, KASLR: Add physical address randomization >4G Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 20/21] x86, KASLR: Remove unused slot tracking code Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook 2016-04-14 22:29 ` [PATCH v5 21/21] x86, KASLR: Allow randomization below load address Kees Cook 2016-04-14 22:29 ` [kernel-hardening] " Kees Cook
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