@@ -1128,6 +1128,14 @@ int sdei_event_handler(struct pt_regs *regs,
mm_segment_t orig_addr_limit;
u32 event_num = arg->event_num;
+ /*
+ * Save restore 'fs'.
+ * The architecture's entry code save/restores 'fs' when taking an
+ * exception from the kernel. This ensures addr_limit isn't inherited
+ * if you interrupted something that allowed the uaccess routines to
+ * access kernel memory.
+ * Do the same here because this doesn't come via the same entry code.
+ */
orig_addr_limit = get_fs();
set_fs(USER_DS);
The SDEI handler save/restores the addr_limit using set_fs(). It isn't very clear why. The reason is to mirror the arch code's entry assembly. The arch code does this because perf may access user-space, and inheriting the addr_limit may be a problem. Add a comment explaining why this is here. Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=822 Suggested-by: Christoph Hellwig <hch@lst.de> Signed-off-by: James Morse <james.morse@arm.com> --- drivers/firmware/arm_sdei.c | 8 ++++++++ 1 file changed, 8 insertions(+)