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arm32/64/elf: Add tables to document READ_IMPLIES_EXEC 

Add tables to document the current behavior of READ_IMPLIES_EXEC in
preparation for changing the behavior for both arm64 and arm.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lkml.kernel.org/r/20200327064820.12602-5-keescook@chromium.org
This commit is contained in:
Kees Cook 2020-03-26 23:48:18 -07:00 committed by Borislav Petkov
parent 9fccc5c0c9
commit 78066055b0
2 changed files with 41 additions and 3 deletions
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24
arch/arm/kernel/elf.c
View File

@ -78,9 +78,27 @@ void elf_set_personality(const struct elf32_hdr *x)
EXPORT_SYMBOL(elf_set_personality);
/*
* Set READ_IMPLIES_EXEC if:
* - the binary requires an executable stack
* - we're running on a CPU which doesn't support NX.
* An executable for which elf_read_implies_exec() returns TRUE will
* have the READ_IMPLIES_EXEC personality flag set automatically.
*
* The decision process for determining the results are:
*
*              CPU: | lacks NX*  | has NX |
* ELF:              |            |           |
* ---------------------|------------|------------|
* missing PT_GNU_STACK | exec-all   | exec-all  |
* PT_GNU_STACK == RWX  | exec-all   | exec-all  |
* PT_GNU_STACK == RW   | exec-all  | exec-none |
*
* exec-all : all PROT_READ user mappings are executable, except when
* backed by files on a noexec-filesystem.
* exec-none : only PROT_EXEC user mappings are executable.
*
* *this column has no architectural effect: NX markings are ignored by
* hardware, but may have behavioral effects when "wants X" collides with
* "cannot be X" constraints in memory permission flags, as in
* https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com
*
*/
int arm_elf_read_implies_exec(int executable_stack)
{

20
arch/arm64/include/asm/elf.h
View File

@ -96,6 +96,26 @@
*/
#define elf_check_arch(x) ((x)->e_machine == EM_AARCH64)
/*
* An executable for which elf_read_implies_exec() returns TRUE will
* have the READ_IMPLIES_EXEC personality flag set automatically.
*
* The decision process for determining the results are:
*
*              CPU*: | arm32    | arm64 |
* ELF:              |            |            |
* ---------------------|------------|------------|
* missing PT_GNU_STACK | exec-all   | exec-all   |
* PT_GNU_STACK == RWX  | exec-all   | exec-all   |
* PT_GNU_STACK == RW   | exec-none | exec-none |
*
* exec-all : all PROT_READ user mappings are executable, except when
* backed by files on a noexec-filesystem.
* exec-none : only PROT_EXEC user mappings are executable.
*
* *all arm64 CPUs support NX, so there is no "lacks NX" column.
*
*/
#define elf_read_implies_exec(ex,stk) (stk != EXSTACK_DISABLE_X)
#define CORE_DUMP_USE_REGSET