arm64: traps: Don't print stack or raw PC/LR values in backtraces

commit a25ffd3a6302a67814280274d8f1aa4ae2ea4b59 upstream.

Printing raw pointer values in backtraces has potential security
implications and are of questionable value anyway.

This patch follows x86's lead and removes the "Exception stack:" dump
from kernel backtraces, as well as converting PC/LR values to symbols
such as "sysrq_handle_crash+0x20/0x30".

Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
[bwh: Backported to 3.16:
 - Deleted code in dump_mem() and dump_backtrace_entry() is a bit different
 - Leave dump_backtrace() unchanged, since it doesn't use dump_mem()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

2 files changed, 4 insertions, 50 deletions

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 291fcb57299d..c965c20864a0 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -198,11 +198,9 @@ void __show_regs(struct pt_regs *regs)
 	}
 
 	show_regs_print_info(KERN_DEFAULT);
-	print_symbol("PC is at %s\n", instruction_pointer(regs));
-	print_symbol("LR is at %s\n", lr);
-	printk("pc : [<%016llx>] lr : [<%016llx>] pstate: %08llx\n",
-	       regs->pc, lr, regs->pstate);
-	printk("sp : %016llx\n", sp);
+	print_symbol("pc : %s\n", regs->pc);
+	print_symbol("lr : %s\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]);
 		if (i % 2 == 0)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index a788b4a32764..463cab118991 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -47,53 +47,9 @@ static const char *handler[]= {
 
 int show_unhandled_signals = 1;
 
-/*
- * Dump out the contents of some memory nicely...
- */
-static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
-		     unsigned long top)
-{
-	unsigned long first;
-	mm_segment_t fs;
-	int i;
-
-	/*
-	 * We need to switch to kernel mode so that we can use __get_user
-	 * to safely read from kernel space.
-	 */
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-
-	printk("%s%s(0x%016lx to 0x%016lx)\n", lvl, str, bottom, top);
-
-	for (first = bottom & ~31; first < top; first += 32) {
-		unsigned long p;
-		char str[sizeof(" 12345678") * 8 + 1];
-
-		memset(str, ' ', sizeof(str));
-		str[sizeof(str) - 1] = '\0';
-
-		for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
-			if (p >= bottom && p < top) {
-				unsigned int val;
-				if (__get_user(val, (unsigned int *)p) == 0)
-					sprintf(str + i * 9, " %08x", val);
-				else
-					sprintf(str + i * 9, " ????????");
-			}
-		}
-		printk("%s%04lx:%s\n", lvl, first & 0xffff, str);
-	}
-
-	set_fs(fs);
-}
-
 static void dump_backtrace_entry(unsigned long where, unsigned long stack)
 {
-	print_ip_sym(where);
-	if (in_exception_text(where))
-		dump_mem("", "Exception stack", stack,
-			 stack + sizeof(struct pt_regs));
+	printk(" %pS\n", (void *)where);
 }
 
 static void __dump_instr(const char *lvl, struct pt_regs *regs)