x86/fsgsbase/64: Report FSBASE and GSBASE correctly in core dumps

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>

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 81a156923b61685d1cdcee3eb68b25ea9857cc19..e67dd21dd9072ea9d68fb4b0e355b67ae3e0d997 100644 (file)
--- 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;       \