2023-07-04 15:48:49

by Florent Revest

Subject: [PATCH v3 3/5] 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: [email protected]
Signed-off-by: Florent Revest <[email protected]>
Suggested-by: Alexey Izbyshev <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
---
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 f23d9a16507f..6e9af6cbc950 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 f23d9a16507f..6e9af6cbc950 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

--
2.41.0.255.g8b1d071c50-goog

2023-07-04 15:59:52

by Florent Revest

Subject: Re: [PATCH v3 3/5] mm: Make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long

On Tue, Jul 4, 2023 at 5:37 PM Florent Revest <[email protected]> wrote:
>
> 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: [email protected]

Oops, this was supposed to be [email protected]... I'll fix that
tag as part of v4.