[tip: core/core] arm64/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces

[tip-bot2 for Kees Cook]

The following commit has been merged into the core/core branch of tip:

Commit-ID:     6e0d6ac5f3d9d90271899f6d340872360fe1caee
Gitweb:        https://git.kernel.org/tip/6e0d6ac5f3d9d90271899f6d340872360fe1caee
Author:        Kees Cook <keescook@xxxxxxxxxxxx>
AuthorDate:    Thu, 26 Mar 2020 23:48:20 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Mon, 20 Apr 2020 19:44:27 +02:00

arm64/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces

With arm64 64-bit environments, there should never be a need for automatic
READ_IMPLIES_EXEC, as the architecture has always been execute-bit aware
(as in, the default memory protection should be NX unless a region
explicitly requests to be executable).

Suggested-by: Hector Marco-Gisbert <hecmargi@xxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Link: https://lkml.kernel.org/r/20200327064820.12602-7-keescook@xxxxxxxxxxxx
---
 arch/arm64/include/asm/elf.h | 4 ++--
 fs/compat_binfmt_elf.c       | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 0074e9f..0e7df6f 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -105,7 +105,7 @@
  * Â Â Â Â Â Â   ÂCPU*: | arm32Â Â   | arm64      |
  * ELF: Â Â Â    Â Â Â Â| Â Â Â Â Â Â| Â Â Â Â Â Â|
  * ---------------------|------------|------------|
- * missing PT_GNU_STACK | exec-all  | exec-all  |
+ * missing PT_GNU_STACK | exec-all  | exec-none |
  * PT_GNU_STACK == RWX Â| exec-stack | exec-stack |
  * PT_GNU_STACK == RW Â | exec-none  | exec-none  |
  *
@@ -117,7 +117,7 @@
  *  *all arm64 CPUs support NX, so there is no "lacks NX" column.
  *
  */
-#define elf_read_implies_exec(ex, stk)	(stk == EXSTACK_DEFAULT)
+#define compat_elf_read_implies_exec(ex, stk)	(stk == EXSTACK_DEFAULT)
 
 #define CORE_DUMP_USE_REGSET
 #define ELF_EXEC_PAGESIZE	PAGE_SIZE
diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c
index aaad4ca..3068d57 100644
--- a/fs/compat_binfmt_elf.c
+++ b/fs/compat_binfmt_elf.c
@@ -113,6 +113,11 @@
 #define	arch_setup_additional_pages compat_arch_setup_additional_pages
 #endif
 
+#ifdef	compat_elf_read_implies_exec
+#undef	elf_read_implies_exec
+#define	elf_read_implies_exec compat_elf_read_implies_exec
+#endif
+
 /*
  * Rename a few of the symbols that binfmt_elf.c will define.
  * These are all local so the names don't really matter, but it