diff options
| author | Paul Burton <paul.burton@mips.com> | 2018-12-20 17:45:43 +0000 |
|---|---|---|
| committer | Paul Burton <paul.burton@mips.com> | 2018-12-20 10:00:01 -0800 |
| commit | adcc81f148d733b7e8e641300c5590a2cdc13bf3 (patch) | |
| tree | 95ae4624fa8b2011aa09d5ac9de40f2eef609110 /arch/mips/kernel | |
| parent | 41e486f4f66d3e646fedd60469bc60e73662de50 (diff) | |
MIPS: math-emu: Write-protect delay slot emulation pages
Mapping the delay slot emulation page as both writeable & executable
presents a security risk, in that if an exploit can write to & jump into
the page then it can be used as an easy way to execute arbitrary code.
Prevent this by mapping the page read-only for userland, and using
access_process_vm() with the FOLL_FORCE flag to write to it from
mips_dsemul().
This will likely be less efficient due to copy_to_user_page() performing
cache maintenance on a whole page, rather than a single line as in the
previous use of flush_cache_sigtramp(). However this delay slot
emulation code ought not to be running in any performance critical paths
anyway so this isn't really a problem, and we can probably do better in
copy_to_user_page() anyway in future.
A major advantage of this approach is that the fix is small & simple to
backport to stable kernels.
Reported-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: 432c6bacbd0c ("MIPS: Use per-mm page to execute branch delay slot instructions")
Cc: stable@vger.kernel.org # v4.8+
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Rich Felker <dalias@libc.org>
Cc: David Daney <david.daney@cavium.com>
Diffstat (limited to 'arch/mips/kernel')
| -rw-r--r-- | arch/mips/kernel/vdso.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c index 48a9c6b90e07..9df3ebdc7b0f 100644 --- a/arch/mips/kernel/vdso.c +++ b/arch/mips/kernel/vdso.c @@ -126,8 +126,8 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) /* Map delay slot emulation page */ base = mmap_region(NULL, STACK_TOP, PAGE_SIZE, - VM_READ|VM_WRITE|VM_EXEC| - VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, + VM_READ | VM_EXEC | + VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC, 0, NULL); if (IS_ERR_VALUE(base)) { ret = base; |