arm64: __show_regs: Only resolve kernel symbols when running at EL1

commit a06f818a70de21b4b3b4186816094208fc7accf9 upstream.

__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.

Reported-by: NCSC Security <security@ncsc.gov.uk>
Signed-off-by: Will Deacon <will.deacon@arm.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 831a45e1f8e47a7a077472b99190ba6fa2ce01dc..0bfb5fe5fdc76de49fc5177ce9d8b6a5de8ae4a4 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -197,8 +197,15 @@ void __show_regs(struct pt_regs *regs)
        }
 
        show_regs_print_info(KERN_DEFAULT);
-       printk("pc : %pS\n", (void *)regs->pc);
-       printk("lr : %pS\n", (void *)lr);
+
+       if (!user_mode(regs)) {
+               printk("pc : %pS\n", (void *)regs->pc);
+               printk("lr : %pS\n", (void *)lr);
+       } else {
+               printk("pc : %016llx\n", regs->pc);
+               printk("lr : %016llx\n", lr);
+       }
+
        printk("sp : %016llx pstate : %08llx\n", sp, regs->pstate);
        for (i = top_reg; i >= 0; i--) {
                printk("x%-2d: %016llx ", i, regs->regs[i]);