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From: Kees Cook <keescook@chromium.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Kees Cook <keescook@chromium.org>,
	Hector Marco-Gisbert <hecmargi@upv.es>,
	Jason Gunthorpe <jgg@mellanox.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Russell King <linux@armlinux.org.uk>,
	Will Deacon <will@kernel.org>, Jann Horn <jannh@google.com>,
	x86@kernel.org, linux-arm-kernel@lists.infradead.org,
	kernel-hardening@lists.openwall.com,
	linux-kernel@vger.kernel.org
Subject: [PATCH v5 3/6] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces
Date: Thu, 26 Mar 2020 23:48:17 -0700
Message-ID: <20200327064820.12602-4-keescook@chromium.org> (raw)
In-Reply-To: <20200327064820.12602-1-keescook@chromium.org>

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>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.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


  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-27  6:48 [PATCH v5 0/6] binfmt_elf: Update READ_IMPLIES_EXEC logic for modern CPUs Kees Cook
2020-03-27  6:48 ` [PATCH v5 1/6] x86/elf: Add table to document READ_IMPLIES_EXEC Kees Cook
2020-03-27  6:48 ` [PATCH v5 2/6] x86/elf: Split READ_IMPLIES_EXEC from executable PT_GNU_STACK Kees Cook
2020-03-27  6:48 ` Kees Cook [this message]
2020-03-27  6:48 ` [PATCH v5 4/6] arm32/64, elf: Add tables to document READ_IMPLIES_EXEC Kees Cook
2020-03-27  6:48 ` [PATCH v5 5/6] arm32/64, elf: Split READ_IMPLIES_EXEC from executable PT_GNU_STACK Kees Cook
2020-03-27  6:48 ` [PATCH v5 6/6] arm64, elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces Kees Cook

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