linux-kernel - [PATCH v4 4/6] mm: Make PR_MDWE_REFUSE_EXEC

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Message-ID: <20230828150858.393570-5-revest@chromium.org>
Date:   Mon, 28 Aug 2023 17:08:56 +0200
From:   Florent Revest <revest@...omium.org>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, catalin.marinas@....com,
        anshuman.khandual@....com, joey.gouly@....com, mhocko@...e.com,
        keescook@...omium.org, david@...hat.com, peterx@...hat.com,
        izbyshev@...ras.ru, broonie@...nel.org, szabolcs.nagy@....com,
        kpsingh@...nel.org, gthelen@...gle.com, toiwoton@...il.com,
        ayush.jain3@....com, Florent Revest <revest@...omium.org>,
        stable@...r.kernel.org
Subject: [PATCH v4 4/6] mm: Make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long

Defining a prctl flag as an int is a footgun because on a 64 bit machine
and with a variadic implementation of prctl (like in musl and glibc),
when used directly as a prctl argument, it can get casted to long with
garbage upper bits which would result in unexpected behaviors.

This patch changes the constant to an unsigned long to eliminate that
possibilities. This does not break UAPI.

Fixes: b507808ebce2 ("mm: implement memory-deny-write-execute as a prctl")
Cc: stable@...r.kernel.org
Signed-off-by: Florent Revest <revest@...omium.org>
Suggested-by: Alexey Izbyshev <izbyshev@...ras.ru>
Reviewed-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Acked-by: Catalin Marinas <catalin.marinas@....com>
---
 include/uapi/linux/prctl.h       | 2 +-
 tools/include/uapi/linux/prctl.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 3c36aeade991..9a85c69782bd 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -283,7 +283,7 @@ struct prctl_mm_map {
 
 /* Memory deny write / execute */
 #define PR_SET_MDWE			65
-# define PR_MDWE_REFUSE_EXEC_GAIN	1
+# define PR_MDWE_REFUSE_EXEC_GAIN	(1UL << 0)
 
 #define PR_GET_MDWE			66
 
diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
index 3c36aeade991..9a85c69782bd 100644
--- a/tools/include/uapi/linux/prctl.h
+++ b/tools/include/uapi/linux/prctl.h
@@ -283,7 +283,7 @@ struct prctl_mm_map {
 
 /* Memory deny write / execute */
 #define PR_SET_MDWE			65
-# define PR_MDWE_REFUSE_EXEC_GAIN	1
+# define PR_MDWE_REFUSE_EXEC_GAIN	(1UL << 0)
 
 #define PR_GET_MDWE			66
 
-- 
2.42.0.rc2.253.gd59a3bf2b4-goog