Re: FAILED: patch "[PATCH] arm64: __show_regs: Only resolve kernel symbols when running" failed to apply to 4.15-stable tree

[Will Deacon <will.deacon@arm.com>]

Hi Greg,

On Mon, Feb 26, 2018 at 04:35:35PM +0100, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 4.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Backport for 4.15 below. The fix isn't relevant to older kernels, since
we don't attempt to resolve kernel symbols here prior to 4.15.

Cheers,

Will

--->8

>From e1b50532bf7e23932fedb243286e900436f3d808 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Mon, 19 Feb 2018 16:46:57 +0000
Subject: [PATCH] arm64: __show_regs: Only resolve kernel symbols when running
 at EL1

__show_regs pretty prints PC and LR by attempting to map them to kernel
function names to improve the utility of crash reports. Unfortunately,
this mapping is applied even when the pt_regs corresponds to user mode,
resulting in a KASLR oracle.

Avoid this issue by only looking up the function symbols when the register
state indicates that we're actually running at EL1.

Cc: <stable@vger.kernel.org> #4.15
Reported-by: NCSC Security <security@ncsc.gov.uk>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm64/kernel/process.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 583fd8154695..d6ca5fccb229 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -221,8 +221,15 @@ void __show_regs(struct pt_regs *regs)
 
 	show_regs_print_info(KERN_DEFAULT);
 	print_pstate(regs);
-	print_symbol("pc : %s\n", regs->pc);
-	print_symbol("lr : %s\n", lr);
+
+	if (!user_mode(regs)) {
+		print_symbol("pc : %s\n", regs->pc);
+		print_symbol("lr : %s\n", lr);
+	} else {
+		printk("pc : %016llx\n", regs->pc);
+		printk("lr : %016llx\n", lr);
+	}
+
 	printk("sp : %016llx\n", sp);
 
 	i = top_reg;
-- 
2.1.4