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Date: Mon, 28 Feb 2022 15:31:00 -0500 From: matoro <matoro_mailinglist_kernel@...oro.tk> To: Kees Cook <keescook@...omium.org> Cc: Alexander Viro <viro@...iv.linux.org.uk>, Eric Biederman <ebiederm@...ssion.com>, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, stable@...r.kernel.org, Thorsten Leemhuis <regressions@...mhuis.info>, Anthony Yznaga <anthony.yznaga@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, regressions@...ts.linux.dev, linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] binfmt_elf: Avoid total_mapping_size for ET_EXEC On 2022-02-28 14:46, 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 <viro@...iv.linux.org.uk> > Cc: Eric Biederman <ebiederm@...ssion.com> > Cc: linux-fsdevel@...r.kernel.org > Cc: linux-mm@...ck.org > Reported-by: matoro <matoro_mailinglist_kernel@...oro.tk> > Reported-by: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de> > Fixes: 5f501d555653 ("binfmt_elf: reintroduce using > MAP_FIXED_NOREPLACE") > Link: > https://lore.kernel.org/r/a3edd529-c42d-3b09-135c-7e98a15b150f@leemhuis.info > Cc: stable@...r.kernel.org > Signed-off-by: Kees Cook <keescook@...omium.org> > --- > matoro (or anyone else) can you please test this? > --- > 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 9bea703ed1c2..474b44032c65 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1136,14 +1136,25 @@ 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 first_pt_load is set to false later once the > - * initial mapping is performed.) > - */ > - if (first_pt_load) { > + /* > + * 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 not apply for me, I'm looking around and can't find any reference to the first_pt_load variable you're removing there? What commit/tag are you applying this on top of?
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