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 <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Yu-cheng Yu <[email protected]>
Link: http://lkml.kernel.org/r/4e36812b6e1e95236a812021d35cbf22746b5af6.1542841400.git.luto@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>

Author: amluto

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);