This is a note to let you know that I've just added the patch titled MIPS: Only change $28 to thread_info if coming from user mode to the 4.10-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: mips-only-change-28-to-thread_info-if-coming-from-user-mode.patch and it can be found in the queue-4.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 510d86362a27577f5ee23f46cfb354ad49731e61 Mon Sep 17 00:00:00 2001 From: Matt Redfearn <matt.redfearn@xxxxxxxxxx> Date: Mon, 19 Dec 2016 14:20:58 +0000 Subject: MIPS: Only change $28 to thread_info if coming from user mode From: Matt Redfearn <matt.redfearn@xxxxxxxxxx> commit 510d86362a27577f5ee23f46cfb354ad49731e61 upstream. The SAVE_SOME macro is used to save the execution context on all exceptions. If an exception occurs while executing user code, the stack is switched to the kernel's stack for the current task, and register $28 is switched to point to the current_thread_info, which is at the bottom of the stack region. If the exception occurs while executing kernel code, the stack is left, and this change ensures that register $28 is not updated. This is the correct behaviour when the kernel can be executing on the separate irq stack, because the thread_info will not be at the base of it. With this change, register $28 is only switched to it's kernel conventional usage of the currrent thread info pointer at the point at which execution enters kernel space. Doing it on every exception was redundant, but OK without an IRQ stack, but will be erroneous once that is introduced. Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxxxx> Acked-by: Jason A. Donenfeld <jason@xxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: James Hogan <james.hogan@xxxxxxxxxx> Cc: Paul Burton <paul.burton@xxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Patchwork: https://patchwork.linux-mips.org/patch/14742/ Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/mips/include/asm/stackframe.h | 7 +++++++ 1 file changed, 7 insertions(+) --- a/arch/mips/include/asm/stackframe.h +++ b/arch/mips/include/asm/stackframe.h @@ -216,12 +216,19 @@ LONG_S $25, PT_R25(sp) LONG_S $28, PT_R28(sp) LONG_S $31, PT_R31(sp) + + /* Set thread_info if we're coming from user mode */ + mfc0 k0, CP0_STATUS + sll k0, 3 /* extract cu0 bit */ + bltz k0, 9f + ori $28, sp, _THREAD_MASK xori $28, _THREAD_MASK #ifdef CONFIG_CPU_CAVIUM_OCTEON .set mips64 pref 0, 0($28) /* Prefetch the current pointer */ #endif +9: .set pop .endm Patches currently in stable-queue which might be from matt.redfearn@xxxxxxxxxx are queue-4.10/mips-only-change-28-to-thread_info-if-coming-from-user-mode.patch queue-4.10/mips-stack-unwinding-while-on-irq-stack.patch queue-4.10/mips-introduce-irq_stack.patch