[tip:x86/mm] x86/oops: Show the correct CS value in show_regs()

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  d38bc89c72e7235ac889ae64fe7828e2e61a18af
Gitweb:     https://git.kernel.org/tip/d38bc89c72e7235ac889ae64fe7828e2e61a18af
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 21 Nov 2018 15:11:24 -0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 22 Nov 2018 09:23:01 +0100

x86/oops: Show the correct CS value in show_regs()

show_regs() shows the CS in the CPU register instead of the value in
regs.  This means that we'll probably print "CS: 0010" almost all
the time regardless of what was actually in CS when the kernel
malfunctioned.  This gives a particularly confusing result if we
OOPSed due to an implicit supervisor access from user mode.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/4e36812b6e1e95236a812021d35cbf22746b5af6.1542841400.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/process_64.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 0e0b4288a4b2..2b8e6324fa20 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -66,7 +66,7 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
 	unsigned long d0, d1, d2, d3, d6, d7;
 	unsigned int fsindex, gsindex;
-	unsigned int ds, cs, es;
+	unsigned int ds, es;
 
 	show_iret_regs(regs);
 
@@ -98,7 +98,6 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 	}
 
 	asm("movl %%ds,%0" : "=r" (ds));
-	asm("movl %%cs,%0" : "=r" (cs));
 	asm("movl %%es,%0" : "=r" (es));
 	asm("movl %%fs,%0" : "=r" (fsindex));
 	asm("movl %%gs,%0" : "=r" (gsindex));
@@ -114,7 +113,7 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 
 	printk(KERN_DEFAULT "FS:  %016lx(%04x) GS:%016lx(%04x) knlGS:%016lx\n",
 	       fs, fsindex, gs, gsindex, shadowgs);
-	printk(KERN_DEFAULT "CS:  %04x DS: %04x ES: %04x CR0: %016lx\n", cs, ds,
+	printk(KERN_DEFAULT "CS:  %04lx DS: %04x ES: %04x CR0: %016lx\n", regs->cs, ds,
 			es, cr0);
 	printk(KERN_DEFAULT "CR2: %016lx CR3: %016lx CR4: %016lx\n", cr2, cr3,
 			cr4);