Patch "MIPS: do_mcheck: Fix kernel code dump with EVA" has been added to the 4.1-stable tree

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

MIPS: do_mcheck: Fix kernel code dump with EVA

to the 4.1-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-do_mcheck-fix-kernel-code-dump-with-eva.patch
and it can be found in the queue-4.1 subdirectory.

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

From: James Hogan <[email protected]>
Date: Mon, 27 Jul 2015 13:50:21 +0100
Subject: MIPS: do_mcheck: Fix kernel code dump with EVA

From: James Hogan <[email protected]>

commit 55c723e181ccec30fb5c672397fe69ec35967d97 upstream.

If a machine check exception is raised in kernel mode, user context, with EVA enabled, then the do_mcheck handler will attempt to read the code around the EPC using EVA load instructions, i.e. as if the reads were from user mode. This will either read random user data if the process has anything mapped at the same address, or it will cause an exception which is handled by __get_user, resulting in this output:

 Code: (Bad address in epc)

Fix by setting the current user access mode to kernel if the saved register context indicates the exception was taken in kernel mode. This causes __get_user to use normal loads to read the kernel code.

Patchwork: https://patchwork.linux-mips.org/patch/10777/

---
 arch/mips/kernel/traps.c |    6 ++++++
 1 file changed, 6 insertions(+)

@@ -1518,6 +1518,7 @@ asmlinkage void do_mcheck(struct pt_regs
 	const int field = 2 * sizeof(unsigned long);
 	int multi_match = regs->cp0_status & ST0_TS;
 	enum ctx_state prev_state;
+	mm_segment_t old_fs = get_fs();
 
 	prev_state = exception_enter();
 	show_regs(regs);

@@ -1539,8 +1540,13 @@ asmlinkage void do_mcheck(struct pt_regs
 		dump_tlb_all();
 	}
 
+	if (!user_mode(regs))
+		set_fs(KERNEL_DS);
+
 	show_code((unsigned int __user *) regs->cp0_epc);
 
+	set_fs(old_fs);
+
 	/*
 	 * Some chips may have other causes of machine check (e.g. SB1
 	 * graduation timer)

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

queue-4.1/mips-show_stack-fix-stack-trace-with-eva.patch queue-4.1/mips-flush-rps-on-kernel-entry-with-eva.patch queue-4.1/mips-do_mcheck-fix-kernel-code-dump-with-eva.patch queue-4.1/mips-malta-don-t-reinitialise-rtc.patch