+ mm-add-debug_wx-support.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: add DEBUG_WX support
has been added to the -mm tree.  Its filename is
     mm-add-debug_wx-support.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-add-debug_wx-support.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-add-debug_wx-support.patch

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------------------------------------------------------
From: Zong Li <zong.li@sifive.com>
Subject: mm: add DEBUG_WX support

Patch series "Extract DEBUG_WX to shared use".

Some architectures support DEBUG_WX function, it's verbatim from each
others, so extract to mm/Kconfig.debug for shared use.

PPC and ARM ports don't support generic page dumper yet, so we only
refine x86 and arm64 port in this patch series.

For RISC-V port, the DEBUG_WX support depends on other patches which
be merged already:
  - RISC-V page table dumper
  - Support strict kernel memory permissions for security


This patch (of 4):

Some architectures support DEBUG_WX function, it's verbatim from each
others.  Extract to mm/Kconfig.debug for shared use.

Link: http://lkml.kernel.org/r/cover.1587455584.git.zong.li@sifive.com
Link: http://lkml.kernel.org/r/23980cd0f0e5d79e24a92169116407c75bcc650d.1587455584.git.zong.li@sifive.com
Signed-off-by: Zong Li <zong.li@sifive.com>
Suggested-by: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/Kconfig.debug |   33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

--- a/mm/Kconfig.debug~mm-add-debug_wx-support
+++ a/mm/Kconfig.debug
@@ -118,6 +118,39 @@ config DEBUG_RODATA_TEST
     ---help---
       This option enables a testcase for the setting rodata read-only.
 
+config ARCH_HAS_DEBUG_WX
+	bool
+
+config DEBUG_WX
+	bool "Warn on W+X mappings at boot"
+	depends on ARCH_HAS_DEBUG_WX
+	select PTDUMP_CORE
+	help
+	  Generate a warning if any W+X mappings are found at boot.
+
+	  This is useful for discovering cases where the kernel is leaving
+	  W+X mappings after applying NX, as such mappings are a security risk.
+	  This check also includes UXN, which should be set on all kernel
+	  mappings.
+
+	  Look for a message in dmesg output like this:
+
+	    <arch>/mm: Checked W+X mappings: passed, no W+X pages found.
+
+	  or like this, if the check failed:
+
+	    <arch>/mm: Checked W+X mappings: failed, <N> W+X pages found.
+
+	  Note that even if the check fails, your kernel is possibly
+	  still fine, as W+X mappings are not a security hole in
+	  themselves, what they do is that they make the exploitation
+	  of other unfixed kernel bugs easier.
+
+	  There is no runtime or memory usage effect of this option
+	  once the kernel has booted up - it's a one time check.
+
+	  If in doubt, say "Y".
+
 config GENERIC_PTDUMP
 	bool
 
_

Patches currently in -mm which might be from zong.li@sifive.com are

mm-add-debug_wx-support.patch
riscv-support-debug_wx.patch
x86-mm-use-arch_has_debug_wx-instead-of-arch-defined.patch
arm64-mm-use-arch_has_debug_wx-instead-of-arch-defined.patch