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authorLinus Torvalds <torvalds@linux-foundation.org>2019-10-06 13:53:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-10-06 13:53:27 -0700
commitb212921b13bda088a004328457c5c21458262fe2 (patch)
tree8f937df8b01f1ea7e13bf8bb87d6ca26190e5b56
parent7cdb85df6061d001fffd09c6adfbcf20356615e2 (diff)
downloadlinux-b212921b13bda088a004328457c5c21458262fe2.tar.gz
elf: don't use MAP_FIXED_NOREPLACE for elf executable mappings
In commit 4ed28639519c ("fs, elf: drop MAP_FIXED usage from elf_map") we changed elf to use MAP_FIXED_NOREPLACE instead of MAP_FIXED for the executable mappings. Then, people reported that it broke some binaries that had overlapping segments from the same file, and commit ad55eac74f20 ("elf: enforce MAP_FIXED on overlaying elf segments") re-instated MAP_FIXED for some overlaying elf segment cases. But only some - despite the summary line of that commit, it only did it when it also does a temporary brk vma for one obvious overlapping case. Now Russell King reports another overlapping case with old 32-bit x86 binaries, which doesn't trigger that limited case. End result: we had better just drop MAP_FIXED_NOREPLACE entirely, and go back to MAP_FIXED. Yes, it's a sign of old binaries generated with old tool-chains, but we do pride ourselves on not breaking existing setups. This still leaves MAP_FIXED_NOREPLACE in place for the load_elf_interp() and the old load_elf_library() use-cases, because nobody has reported breakage for those. Yet. Note that in all the cases seen so far, the overlapping elf sections seem to be just re-mapping of the same executable with different section attributes. We could possibly introduce a new MAP_FIXED_NOFILECHANGE flag or similar, which acts like NOREPLACE, but allows just remapping the same executable file using different protection flags. It's not clear that would make a huge difference to anything, but if people really hate that "elf remaps over previous maps" behavior, maybe at least a more limited form of remapping would alleviate some concerns. Alternatively, we should take a look at our elf_map() logic to see if we end up not mapping things properly the first time. In the meantime, this is the minimal "don't do that then" patch while people hopefully think about it more. Reported-by: Russell King <linux@armlinux.org.uk> Fixes: 4ed28639519c ("fs, elf: drop MAP_FIXED usage from elf_map") Fixes: ad55eac74f20 ("elf: enforce MAP_FIXED on overlaying elf segments") Cc: Michal Hocko <mhocko@suse.com> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/binfmt_elf.c13
1 files changed, 3 insertions, 10 deletions
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index ad4c6b1d5074..c5642bcb6b46 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -879,7 +879,7 @@ out_free_interp:
the correct location in memory. */
for(i = 0, elf_ppnt = elf_phdata;
i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
- int elf_prot, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
+ int elf_prot, elf_flags;
unsigned long k, vaddr;
unsigned long total_size = 0;
@@ -911,13 +911,6 @@ out_free_interp:
*/
}
}
-
- /*
- * Some binaries have overlapping elf segments and then
- * we have to forcefully map over an existing mapping
- * e.g. over this newly established brk mapping.
- */
- elf_fixed = MAP_FIXED;
}
elf_prot = make_prot(elf_ppnt->p_flags);
@@ -930,7 +923,7 @@ out_free_interp:
* the ET_DYN load_addr calculations, proceed normally.
*/
if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
- elf_flags |= elf_fixed;
+ elf_flags |= MAP_FIXED;
} else if (loc->elf_ex.e_type == ET_DYN) {
/*
* This logic is run once for the first LOAD Program
@@ -966,7 +959,7 @@ out_free_interp:
load_bias = ELF_ET_DYN_BASE;
if (current->flags & PF_RANDOMIZE)
load_bias += arch_mmap_rnd();
- elf_flags |= elf_fixed;
+ elf_flags |= MAP_FIXED;
} else
load_bias = 0;