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x86/elf: Disable automatic READ_IMPLIES_EXEC on 64-bit

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With modern x86 64-bit environments, there should never be a need for
automatic READ_IMPLIES_EXEC, as the architecture is intended to always
be execute-bit aware (as in, the default memory protection should be NX
unless a region explicitly requests to be executable).

There were very old x86_64 systems that lacked the NX bit, but for those,
the NX bit is, obviously, unenforceable, so these changes should have
no impact on them.

Suggested-by: Hector Marco-Gisbert <hecmargi@upv.es>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Link: https://lkml.kernel.org/r/20200327064820.12602-4-keescook@chromium.org
This commit is contained in:
Kees Cook 2020-03-26 23:48:17 -07:00 committed by Borislav Petkov
parent 122306117a
commit 9fccc5c0c9
1 changed files with 2 additions and 2 deletions
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4
arch/x86/include/asm/elf.h
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@ -287,7 +287,7 @@ extern u32 elf_hwcap2;
*              CPU: | lacks NX*  | has NX, ia32     | has NX, x86_64 |
* ELF:              |            |                  |                |
* ---------------------|------------|------------------|----------------|
* missing PT_GNU_STACK | exec-all   | exec-all         | exec-all       |
* missing PT_GNU_STACK | exec-all   | exec-all         | exec-none      |
* PT_GNU_STACK == RWX  | exec-stack | exec-stack       | exec-stack     |
* PT_GNU_STACK == RW   | exec-none  | exec-none        | exec-none      |
*
@ -303,7 +303,7 @@ extern u32 elf_hwcap2;
*
*/
#define elf_read_implies_exec(ex, executable_stack) \
(executable_stack == EXSTACK_DEFAULT)
(mmap_is_ia32() && executable_stack == EXSTACK_DEFAULT)
struct task_struct;