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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 v4 3/6] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces
Date: Mon, 24 Feb 2020 21:13:04 -0800	[thread overview]
Message-ID: <20200225051307.6401-4-keescook@chromium.org> (raw)
In-Reply-To: <20200225051307.6401-1-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 a7035065377c..c9b7be0bcad3 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 GNU_STACK | exec-all   | exec-all         | exec-all       |
+ * missing GNU_STACK | exec-all   | exec-all         | exec-none      |
  * GNU_STACK == RWX  | exec-stack | exec-stack       | exec-stack     |
  * 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


WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	x86@kernel.org, Hector Marco-Gisbert <hecmargi@upv.es>,
	Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org, Jason Gunthorpe <jgg@ziepe.ca>,
	Jason Gunthorpe <jgg@mellanox.com>,
	kernel-hardening@lists.openwall.com,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v4 3/6] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces
Date: Mon, 24 Feb 2020 21:13:04 -0800	[thread overview]
Message-ID: <20200225051307.6401-4-keescook@chromium.org> (raw)
In-Reply-To: <20200225051307.6401-1-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 a7035065377c..c9b7be0bcad3 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 GNU_STACK | exec-all   | exec-all         | exec-all       |
+ * missing GNU_STACK | exec-all   | exec-all         | exec-none      |
  * GNU_STACK == RWX  | exec-stack | exec-stack       | exec-stack     |
  * 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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  parent reply	other threads:[~2020-02-25  5:13 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-25  5:13 [PATCH v4 0/6] binfmt_elf: Update READ_IMPLIES_EXEC logic for modern CPUs Kees Cook
2020-02-25  5:13 ` Kees Cook
2020-02-25  5:13 ` [PATCH v4 1/6] x86/elf: Add table to document READ_IMPLIES_EXEC Kees Cook
2020-02-25  5:13   ` Kees Cook
2020-03-11 19:44   ` Borislav Petkov
2020-03-11 19:44     ` Borislav Petkov
2020-03-13  0:06     ` Kees Cook
2020-03-13  0:06       ` Kees Cook
2020-02-25  5:13 ` [PATCH v4 2/6] x86/elf: Split READ_IMPLIES_EXEC from executable GNU_STACK Kees Cook
2020-02-25  5:13   ` Kees Cook
2020-02-25  5:13 ` Kees Cook [this message]
2020-02-25  5:13   ` [PATCH v4 3/6] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces Kees Cook
2020-02-25  5:13 ` [PATCH v4 4/6] arm32/64, elf: Add tables to document READ_IMPLIES_EXEC Kees Cook
2020-02-25  5:13   ` Kees Cook
2020-02-25  5:13 ` [PATCH v4 5/6] arm32/64, elf: Split READ_IMPLIES_EXEC from executable GNU_STACK Kees Cook
2020-02-25  5:13   ` Kees Cook
2020-02-25  5:13 ` [PATCH v4 6/6] arm64, elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces Kees Cook
2020-02-25  5:13   ` Kees Cook

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