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prctl: generalize PR_SET_MDWE support check to be per-arch

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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 793838138c, "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@bewilderbeest.net
Link: https://lkml.kernel.org/r/20240227013546.15769-5-zev@bewilderbeest.net
Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Acked-by: Helge Deller <deller@gmx.de>	[parisc]
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Russell King (Oracle) <linux@armlinux.org.uk>
Cc: Sam James <sam@gentoo.org>
Cc: Stefan Roesch <shr@devkernel.io>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Cc: <stable@vger.kernel.org>	[6.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zev Weiss 2024-02-26 17:35:41 -08:00 committed by Andrew Morton
parent db09f2df91
commit d5aad4c2ca
3 changed files with 27 additions and 2 deletions
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14
arch/parisc/include/asm/mman.h Normal file
View File

@ -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__ */

8
include/linux/mman.h
View File

@ -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.
*

7
kernel/sys.c
View File

@ -2408,8 +2408,11 @@ static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3,
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();