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From: Kees Cook <keescook@chromium.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Kees Cook <keescook@chromium.org>,
	Jason Gunthorpe <jgg@mellanox.com>,
	Hector Marco-Gisbert <hecmargi@upv.es>,
	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 1/6] x86/elf: Add table to document READ_IMPLIES_EXEC
Date: Thu, 26 Mar 2020 23:48:15 -0700
Message-ID: <20200327064820.12602-2-keescook@chromium.org> (raw)
In-Reply-To: <20200327064820.12602-1-keescook@chromium.org>

Add a table to document the current behavior of READ_IMPLIES_EXEC in
preparation for changing the behavior.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
---
 arch/x86/include/asm/elf.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 69c0f892e310..ee459d4c3b45 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -281,6 +281,25 @@ extern u32 elf_hwcap2;
 /*
  * 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, ia32     | has NX, x86_64 |
+ * ELF:                 |            |                  |                |
+ * ---------------------|------------|------------------|----------------|
+ * missing PT_GNU_STACK | exec-all   | exec-all         | exec-all       |
+ * PT_GNU_STACK == RWX  | exec-all   | exec-all         | exec-all       |
+ * PT_GNU_STACK == RW   | exec-none  | 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.
+ *
+ *  *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
+ *
  */
 #define elf_read_implies_exec(ex, executable_stack)	\
 	(executable_stack != EXSTACK_DISABLE_X)
-- 
2.20.1


  reply index

Thread overview: 13+ 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 ` Kees Cook [this message]
2020-04-20 20:03   ` [tip: core/core] x86/elf: Add table to document READ_IMPLIES_EXEC tip-bot2 for Kees Cook
2020-03-27  6:48 ` [PATCH v5 2/6] x86/elf: Split READ_IMPLIES_EXEC from executable PT_GNU_STACK Kees Cook
2020-04-20 20:03   ` [tip: core/core] " tip-bot2 for Kees Cook
2020-03-27  6:48 ` [PATCH v5 3/6] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces Kees Cook
2020-04-20 20:03   ` [tip: core/core] x86/elf: Disable automatic READ_IMPLIES_EXEC on 64-bit tip-bot2 for Kees Cook
2020-03-27  6:48 ` [PATCH v5 4/6] arm32/64, elf: Add tables to document READ_IMPLIES_EXEC Kees Cook
2020-04-20 20:03   ` [tip: core/core] arm32/64/elf: " tip-bot2 for 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
2020-04-20 20:03   ` [tip: core/core] arm32/64/elf: " tip-bot2 for 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
2020-04-20 20:03   ` [tip: core/core] arm64/elf: " tip-bot2 for Kees Cook

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