linux-kernel - [PATCH] x86/dumpstack: Don't mention RIP in "Code:"

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Message-Id: <20220906071123.558-1-jslaby@suse.cz>
Date:   Tue,  6 Sep 2022 09:11:23 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     bp@...e.de
Cc:     tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>,
        Mark Mossberg <mark.mossberg@...il.com>
Subject: [PATCH] x86/dumpstack: Don't mention RIP in "Code:"

Commit 238c91115cd0 ("x86/dumpstack: Fix misleading instruction pointer
error message") changed the "Code:" line in bug reports when RIP is an
invalid pointer. In particular, the report currently says (for example):

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  ...
  RIP: 0010:0x0
  Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.

That "Unable to access opcode bytes at RIP 0xffffffffffffffd6." is
quite confusing as RIP value is 0, not -42. That -42 comes from
"regs->ip - PROLOGUE_SIZE", because Code is dumped with some prologue
(and epilogue).

So do not mention "RIP" on this line in this context.

Cc: Mark Mossberg <mark.mossberg@...il.com>
Cc: Borislav Petkov <bp@...e.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/kernel/dumpstack.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index afae4dd77495..b3dba35f466e 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -128,7 +128,7 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
 		/* No access to the user space stack of other tasks. Ignore. */
 		break;
 	default:
-		printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n",
+		printk("%sCode: Unable to access opcode bytes at 0x%lx.\n",
 		       loglvl, prologue);
 		break;
 	}
-- 
2.37.3