This is a note to let you know that I've just added the patch titled
prctl: generalize PR_SET_MDWE support check to be per-arch
to the 6.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
prctl-generalize-pr_set_mdwe-support-check-to-be-per-arch.patch
and it can be found in the queue-6.7 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From d5aad4c2ca057e760a92a9a7d65bd38d72963f27 Mon Sep 17 00:00:00 2001
From: Zev Weiss <zev@xxxxxxxxxxxxxxxxx>
Date: Mon, 26 Feb 2024 17:35:41 -0800
Subject: prctl: generalize PR_SET_MDWE support check to be per-arch
From: Zev Weiss <zev@xxxxxxxxxxxxxxxxx>
commit d5aad4c2ca057e760a92a9a7d65bd38d72963f27 upstream.
Patch series "ARM: prctl: Reject PR_SET_MDWE where not supported".
I noticed after a recent kernel update that my ARM926 system started
segfaulting on any execve() after calling prctl(PR_SET_MDWE). After some
investigation it appears that ARMv5 is incapable of providing the
appropriate protections for MDWE, since any readable memory is also
implicitly executable.
The prctl_set_mdwe() function already had some special-case logic added
disabling it on PARISC (commit 793838138c15, "prctl: Disable
prctl(PR_SET_MDWE) on parisc"); this patch series (1) generalizes that
check to use an arch_*() function, and (2) adds a corresponding override
for ARM to disable MDWE on pre-ARMv6 CPUs.
With the series applied, prctl(PR_SET_MDWE) is rejected on ARMv5 and
subsequent execve() calls (as well as mmap(PROT_READ|PROT_WRITE)) can
succeed instead of unconditionally failing; on ARMv6 the prctl works as it
did previously.
[0] https://lore.kernel.org/all/2023112456-linked-nape-bf19@gregkh/
This patch (of 2):
There exist systems other than PARISC where MDWE may not be feasible to
support; rather than cluttering up the generic code with additional
arch-specific logic let's add a generic function for checking MDWE support
and allow each arch to override it as needed.
Link: https://lkml.kernel.org/r/20240227013546.15769-4-zev@xxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20240227013546.15769-5-zev@xxxxxxxxxxxxxxxxx
Signed-off-by: Zev Weiss <zev@xxxxxxxxxxxxxxxxx>
Acked-by: Helge Deller <deller@xxxxxx> [parisc]
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Florent Revest <revest@xxxxxxxxxxxx>
Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Miguel Ojeda <ojeda@xxxxxxxxxx>
Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Cc: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Cc: Russell King (Oracle) <linux@xxxxxxxxxxxxxxx>
Cc: Sam James <sam@xxxxxxxxxx>
Cc: Stefan Roesch <shr@xxxxxxxxxxxx>
Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [6.3+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/parisc/include/asm/mman.h | 14 ++++++++++++++
include/linux/mman.h | 8 ++++++++
kernel/sys.c | 7 +++++--
3 files changed, 27 insertions(+), 2 deletions(-)
create mode 100644 arch/parisc/include/asm/mman.h
--- /dev/null
+++ b/arch/parisc/include/asm/mman.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMAN_H__
+#define __ASM_MMAN_H__
+
+#include <uapi/asm/mman.h>
+
+/* PARISC cannot allow mdwe as it needs writable stacks */
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+ return false;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+
+#endif /* __ASM_MMAN_H__ */
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -162,6 +162,14 @@ calc_vm_flag_bits(unsigned long flags)
unsigned long vm_commit_limit(void);
+#ifndef arch_memory_deny_write_exec_supported
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+ return true;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+#endif
+
/*
* Denies creating a writable executable mapping or gaining executable permissions.
*
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2408,8 +2408,11 @@ static inline int prctl_set_mdwe(unsigne
if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN))
return -EINVAL;
- /* PARISC cannot allow mdwe as it needs writable stacks */
- if (IS_ENABLED(CONFIG_PARISC))
+ /*
+ * EOPNOTSUPP might be more appropriate here in principle, but
+ * existing userspace depends on EINVAL specifically.
+ */
+ if (!arch_memory_deny_write_exec_supported())
return -EINVAL;
current_bits = get_current_mdwe();
Patches currently in stable-queue which might be from zev@xxxxxxxxxxxxxxxxx are
queue-6.7/prctl-generalize-pr_set_mdwe-support-check-to-be-per-arch.patch
queue-6.7/arm-prctl-reject-pr_set_mdwe-on-pre-armv6.patch
