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

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Message-ID: <20201009075957.110017-1-nixiaoming@huawei.com>
Date:   Fri, 9 Oct 2020 15:59:57 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     <linux@...linux.org.uk>, <dima@...sta.com>, <will@...nel.org>,
        <jpoimboe@...hat.com>, <akpm@...ux-foundation.org>,
        <christian.brauner@...ntu.com>, <viro@...iv.linux.org.uk>,
        <ldufour@...ux.ibm.com>, <amanieu@...il.com>, <walken@...gle.com>,
        <ben.dooks@...ethink.co.uk>, <tglx@...utronix.de>,
        <bigeasy@...utronix.de>, <mingo@...nel.org>,
        <vincent.whitchurch@...s.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <nixiaoming@...wei.com>,
        <wangle6@...wei.com>, <luohaizheng@...wei.com>
Subject: [PATCH] arm:traps: Don't print stack or raw PC/LR values in backtraces

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

This patch follows x86 and arm64's lead and removes the "Exception stack:"
dump from kernel backtraces:
	commit a25ffd3a6302a6 ("arm64: traps: Don't print stack or raw
	 PC/LR values in backtraces")
	commit 0ee1dd9f5e7eae ("x86/dumpstack: Remove raw stack dump")
	commit bb5e5ce545f203 ("x86/dumpstack: Remove kernel text
	 addresses from stack dump")

Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
---
 arch/arm/kernel/process.c |  3 +--
 arch/arm/kernel/traps.c   | 12 +++++-------
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 8e6ace03e960..71c9e5597d39 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -121,8 +121,7 @@ void __show_regs(struct pt_regs *regs)
 
 	printk("PC is at %pS\n", (void *)instruction_pointer(regs));
 	printk("LR is at %pS\n", (void *)regs->ARM_lr);
-	printk("pc : [<%08lx>]    lr : [<%08lx>]    psr: %08lx\n",
-	       regs->ARM_pc, regs->ARM_lr, regs->ARM_cpsr);
+	printk("psr: %08lx\n", regs->ARM_cpsr);
 	printk("sp : %08lx  ip : %08lx  fp : %08lx\n",
 	       regs->ARM_sp, regs->ARM_ip, regs->ARM_fp);
 	printk("r10: %08lx  r9 : %08lx  r8 : %08lx\n",
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 17d5a785df28..b0b188e01070 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -60,23 +60,18 @@ static int __init user_debug_setup(char *str)
 __setup("user_debug=", user_debug_setup);
 #endif
 
-static void dump_mem(const char *, const char *, unsigned long, unsigned long);
-
 void dump_backtrace_entry(unsigned long where, unsigned long from,
 			  unsigned long frame, const char *loglvl)
 {
 	unsigned long end = frame + 4 + sizeof(struct pt_regs);
 
 #ifdef CONFIG_KALLSYMS
-	printk("%s[<%08lx>] (%ps) from [<%08lx>] (%pS)\n",
-		loglvl, where, (void *)where, from, (void *)from);
+	printk("%s (%ps) from (%pS)\n",
+		loglvl, (void *)where, (void *)from);
 #else
 	printk("%sFunction entered at [<%08lx>] from [<%08lx>]\n",
 		loglvl, where, from);
 #endif
-
-	if (in_entry_text(from) && end <= ALIGN(frame, THREAD_SIZE))
-		dump_mem(loglvl, "Exception stack", frame + 4, end);
 }
 
 void dump_backtrace_stm(u32 *stack, u32 instruction, const char *loglvl)
@@ -125,6 +120,9 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
 	mm_segment_t fs;
 	int i;
 
+	/* Do not print virtual addresses in non-reset scenarios */
+	if (!panic_on_oops)
+		return;
 	/*
 	 * We need to switch to kernel mode so that we can use __get_user
 	 * to safely read from kernel space.  Note that we now dump the
-- 
2.27.0