From mboxrd@z Thu Jan 1 00:00:00 1970 From: matoro Date: Mon, 28 Feb 2022 22:14:26 +0000 Subject: Re: [PATCH 5.16 v2] binfmt_elf: Avoid total_mapping_size for ET_EXEC Message-Id: List-Id: References: <20220228205518.1265798-1-keescook@chromium.org> In-Reply-To: <20220228205518.1265798-1-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Kees Cook Cc: Alexander Viro , Eric Biederman , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, John Paul Adrian Glaubitz , stable@vger.kernel.org, =?UTF-8?Q?Magnus_Gro=C3=9F?= , Thorsten Leemhuis , Anthony Yznaga , Andrew Morton , regressions@lists.linux.dev, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org On 2022-02-28 15:55, Kees Cook wrote: > Partially revert commit 5f501d555653 ("binfmt_elf: reintroduce using > MAP_FIXED_NOREPLACE"). > > At least ia64 has ET_EXEC PT_LOAD segments that are not virtual-address > contiguous (but _are_ file-offset contiguous). This would result in > giant mapping attempts to cover the entire span, including the virtual > address range hole. Disable total_mapping_size for ET_EXEC, which > reduces the MAP_FIXED_NOREPLACE coverage to only the first PT_LOAD: > > $ readelf -lW /usr/bin/gcc > ... > Program Headers: > Type Offset VirtAddr PhysAddr FileSiz MemSiz > ... > ... > LOAD 0x000000 0x4000000000000000 0x4000000000000000 0x00b5a0 0x00b5a0 > ... > LOAD 0x00b5a0 0x600000000000b5a0 0x600000000000b5a0 0x0005ac 0x000710 > ... > ... > ^^^^^^^^ ^^^^^^^^^^^^^^^^^^ ^^^^^^^^ ^^^^^^^^ > > File offset range : 0x000000-0x00bb4c > 0x00bb4c bytes > > Virtual address range : 0x4000000000000000-0x600000000000bcb0 > 0x200000000000bcb0 bytes > > Ironically, this is the reverse of the problem that originally caused > problems with ET_EXEC and MAP_FIXED_NOREPLACE: overlaps. This problem > is > with holes. Future work could restore full coverage if > load_elf_binary() > were to perform mappings in a separate phase from the loading (where > it could resolve both overlaps and holes). > > Cc: Alexander Viro > Cc: Eric Biederman > Cc: linux-fsdevel@vger.kernel.org > Cc: linux-mm@kvack.org > Reported-by: matoro > Reported-by: John Paul Adrian Glaubitz > Fixes: 5f501d555653 ("binfmt_elf: reintroduce using > MAP_FIXED_NOREPLACE") > Link: > https://lore.kernel.org/r/a3edd529-c42d-3b09-135c-7e98a15b150f@leemhuis.info > Cc: stable@vger.kernel.org > Signed-off-by: Kees Cook > --- > Here's the v5.16 backport. > --- > fs/binfmt_elf.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index f8c7f26f1fbb..911a9e7044f4 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1135,14 +1135,25 @@ static int load_elf_binary(struct linux_binprm > *bprm) > * is then page aligned. > */ > load_bias = ELF_PAGESTART(load_bias - vaddr); > - } > > - /* > - * Calculate the entire size of the ELF mapping (total_size). > - * (Note that load_addr_set is set to true later once the > - * initial mapping is performed.) > - */ > - if (!load_addr_set) { > + /* > + * Calculate the entire size of the ELF mapping > + * (total_size), used for the initial mapping, > + * due to first_pt_load which is set to false later > + * once the initial mapping is performed. > + * > + * Note that this is only sensible when the LOAD > + * segments are contiguous (or overlapping). If > + * used for LOADs that are far apart, this would > + * cause the holes between LOADs to be mapped, > + * running the risk of having the mapping fail, > + * as it would be larger than the ELF file itself. > + * > + * As a result, only ET_DYN does this, since > + * some ET_EXEC (e.g. ia64) may have virtual > + * memory holes between LOADs. > + * > + */ > total_size = total_mapping_size(elf_phdata, > elf_ex->e_phnum); > if (!total_size) { This does the trick! Thank you so much!!