[PATCH 3.2 07/61] x86/fsgsbase/64: Report FSBASE and GSBASE correctly in core dumps

[Ben Hutchings <ben@decadent.org.uk>]

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

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

From: Andy Lutomirski <luto@kernel.org>

commit 9584d98bed7a7a904d0702ad06bbcc94703cb5b4 upstream.

In ELF_COPY_CORE_REGS, we're copying from the current task, so
accessing thread.fsbase and thread.gsbase makes no sense.  Just read
the values from the CPU registers.

In practice, the old code would have been correct most of the time
simply because thread.fsbase and thread.gsbase usually matched the
CPU registers.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang Seok <chang.seok.bae@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 arch/x86/include/asm/elf.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -192,6 +192,7 @@ void set_personality_ia32(void);
 
 #define ELF_CORE_COPY_REGS(pr_reg, regs)			\
 do {								\
+	unsigned long base;					\
 	unsigned v;						\
 	(pr_reg)[0] = (regs)->r15;				\
 	(pr_reg)[1] = (regs)->r14;				\
@@ -214,8 +215,8 @@ do {								\
 	(pr_reg)[18] = (regs)->flags;				\
 	(pr_reg)[19] = (regs)->sp;				\
 	(pr_reg)[20] = (regs)->ss;				\
-	(pr_reg)[21] = current->thread.fs;			\
-	(pr_reg)[22] = current->thread.gs;			\
+	rdmsrl(MSR_FS_BASE, base); (pr_reg)[21] = base;		\
+	rdmsrl(MSR_KERNEL_GS_BASE, base); (pr_reg)[22] = base;	\
 	asm("movl %%ds,%0" : "=r" (v)); (pr_reg)[23] = v;	\
 	asm("movl %%es,%0" : "=r" (v)); (pr_reg)[24] = v;	\
 	asm("movl %%fs,%0" : "=r" (v)); (pr_reg)[25] = v;	\