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mm: make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long

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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.

I think that a stable backport would be "nice to have": to reduce the
chances that users build binaries that could end up with garbage bits in
their MDWE prctl arguments.  We are not aware of anyone having yet
encountered this corner case with MDWE prctls but a backport would reduce
the likelihood it happens, since this sort of issues has happened with
other prctls.  But If this is perceived as a backporting burden, I suppose
we could also live without a stable backport.

Link: https://lkml.kernel.org/r/20230828150858.393570-5-revest@chromium.org
Fixes: b507808ebc ("mm: implement memory-deny-write-execute as a prctl")
Signed-off-by: Florent Revest <revest@chromium.org>
Suggested-by: Alexey Izbyshev <izbyshev@ispras.ru>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ayush Jain <ayush.jain3@amd.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc: Topi Miettinen <toiwoton@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Florent Revest 2023-08-28 17:08:56 +02:00 committed by Andrew Morton
parent c93d05a729
commit 0da668333f
2 changed files with 2 additions and 2 deletions
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2
include/uapi/linux/prctl.h
View File

@ -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
tools/include/uapi/linux/prctl.h
View File

@ -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