linux-kernel - [PATCH 3.16 266/410] arm64: traps: Don't print stack or raw PC/LR values in backtraces

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Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Will Deacon" <will.deacon@....com>,
        "Laura Abbott" <labbott@...hat.com>
Subject: [PATCH 3.16 266/410] arm64: traps: Don't print stack or raw PC/LR
 values in backtraces

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@....com>

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@...hat.com>
Signed-off-by: Will Deacon <will.deacon@....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@...adent.org.uk>
---
--- 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)
--- 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)