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Message-Id: <20200327064820.12602-4-keescook@chromium.org>
Date: Thu, 26 Mar 2020 23:48:17 -0700
From: Kees Cook <keescook@...omium.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Kees Cook <keescook@...omium.org>,
Hector Marco-Gisbert <hecmargi@....es>,
Jason Gunthorpe <jgg@...lanox.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Catalin Marinas <catalin.marinas@....com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will@...nel.org>,
Jann Horn <jannh@...gle.com>,
x86@...nel.org,
linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org
Subject: [PATCH v5 3/6] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces
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@....es>
Signed-off-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Jason Gunthorpe <jgg@...lanox.com>
---
arch/x86/include/asm/elf.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 397a1c74433e..452beed7892b 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -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;
--
2.20.1
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