Patch "x86/fsgsbase/64: Report FSBASE and GSBASE correctly in core dumps" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-fsgsbase-64-report-fsbase-and-gsbase-correctly-in-core-dumps.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andy Lutomirski <[email protected]>
Date: Tue, 1 Aug 2017 07:11:35 -0700
Subject: x86/fsgsbase/64: Report FSBASE and GSBASE correctly in core dumps

From: Andy Lutomirski <[email protected]>

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.

---
 arch/x86/include/asm/elf.h |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -204,6 +204,7 @@ void set_personality_ia32(bool);
 
 #define ELF_CORE_COPY_REGS(pr_reg, regs)			\
 do {								\
+	unsigned long base;					\
 	unsigned v;						\
 	(pr_reg)[0] = (regs)->r15;				\
 	(pr_reg)[1] = (regs)->r14;				\

@@ -226,8 +227,8 @@ do {								\
 	(pr_reg)[18] = (regs)->flags;				\
 	(pr_reg)[19] = (regs)->sp;				\
 	(pr_reg)[20] = (regs)->ss;				\
-	(pr_reg)[21] = current->thread.fsbase;			\
-	(pr_reg)[22] = current->thread.gsbase;			\
+	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;	\

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-switch_to-64-rewrite-fs-gs-switching-yet-again-to-fix-amd-cpus.patch queue-4.9/x86-fsgsbase-64-fully-initialize-fs-and-gs-state-in-start_thread_common.patch queue-4.9/x86-fsgsbase-64-report-fsbase-and-gsbase-correctly-in-core-dumps.patch