Patch "arm64: Preventing READ_IMPLIES_EXEC propagation" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

arm64: Preventing READ_IMPLIES_EXEC propagation

to the 4.12-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:
arm64-preventing-read_implies_exec-propagation.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dong Bo <[email protected]>
Date: Tue, 25 Apr 2017 14:11:29 +0800
Subject: arm64: Preventing READ_IMPLIES_EXEC propagation

From: Dong Bo <[email protected]>

commit 48f99c8ec0b25756d0283ab058826ae07d14fad7 upstream.

Like arch/arm/, we inherit the READ_IMPLIES_EXEC personality flag across fork(). This is undesirable for a number of reasons:

* ELF files that don't require executable stack can end up with it anyway

* We end up performing un-necessary I-cache maintenance when mapping what should be non-executable pages

* Restricting what is executable is generally desirable when defending against overflow attacks

This patch clears the personality flag when setting up the personality for newly spwaned native tasks. Given that semi-recent AArch64 toolchains emit a non-executable PT_GNU_STACK header, userspace applications can already not rely on READ_IMPLIES_EXEC so shouldn't be adversely affected by this change.

---
 arch/arm64/include/asm/elf.h |    6 ++++++
 1 file changed, 6 insertions(+)

@@ -141,6 +141,7 @@ typedef struct user_fpsimd_state elf_fpr
 ({									\
 	clear_bit(TIF_32BIT, &current->mm->context.flags);		\
 	clear_thread_flag(TIF_32BIT);					\
+	current->personality &= ~READ_IMPLIES_EXEC;			\
 })
 
 /* update AT_VECTOR_SIZE_ARCH if the number of NEW_AUX_ENT entries changes */

@@ -187,6 +188,11 @@ typedef compat_elf_greg_t		compat_elf_gr
 					 ((x)->e_flags & EF_ARM_EABI_MASK))
 
 #define compat_start_thread		compat_start_thread
+/*
+ * Unlike the native SET_PERSONALITY macro, the compat version inherits
+ * READ_IMPLIES_EXEC across a fork() since this is the behaviour on
+ * arch/arm/.
+ */
 #define COMPAT_SET_PERSONALITY(ex)					\
 ({									\
 	set_bit(TIF_32BIT, &current->mm->context.flags);		\

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/arm64-preventing-read_implies_exec-propagation.patch