4 files changed, 117 insertions, 25 deletions
diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index ee4df08feee6..fbf2f33e3080 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -75,6 +75,7 @@ void foo(void)
 	OFFSET(PT_DS,  pt_regs, ds);
 	OFFSET(PT_ES,  pt_regs, es);
 	OFFSET(PT_FS,  pt_regs, fs);
+	OFFSET(PT_GS,  pt_regs, gs);
 	OFFSET(PT_ORIG_EAX, pt_regs, orig_ax);
 	OFFSET(PT_EIP, pt_regs, ip);
 	OFFSET(PT_CS,  pt_regs, cs);
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index c461925d3b64..82e6868bee47 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -30,12 +30,13 @@
  *	1C(%esp) - %ds
  *	20(%esp) - %es
  *	24(%esp) - %fs
- *	28(%esp) - orig_eax
- *	2C(%esp) - %eip
- *	30(%esp) - %cs
- *	34(%esp) - %eflags
- *	38(%esp) - %oldesp
- *	3C(%esp) - %oldss
+ *	28(%esp) - %gs		saved iff !CONFIG_X86_32_LAZY_GS
+ *	2C(%esp) - orig_eax
+ *	30(%esp) - %eip
+ *	34(%esp) - %cs
+ *	38(%esp) - %eflags
+ *	3C(%esp) - %oldesp
+ *	40(%esp) - %oldss
  *
  * "current" is in register %ebx during any slow entries.
  */
@@ -101,8 +102,99 @@
 #define resume_userspace_sig	resume_userspace
 #endif
 
+/*
+ * User gs save/restore
+ *
+ * %gs is used for userland TLS and kernel only uses it for stack
+ * canary which is required to be at %gs:20 by gcc.  Read the comment
+ * at the top of stackprotector.h for more info.
+ *
+ * Local labels 98 and 99 are used.
+ */
+#ifdef CONFIG_X86_32_LAZY_GS
+
+ /* unfortunately push/pop can't be no-op */
+.macro PUSH_GS
+	pushl $0
+	CFI_ADJUST_CFA_OFFSET 4
+.endm
+.macro POP_GS pop=0
+	addl $(4 + \pop), %esp
+	CFI_ADJUST_CFA_OFFSET -(4 + \pop)
+.endm
+.macro POP_GS_EX
+.endm
+
+ /* all the rest are no-op */
+.macro PTGS_TO_GS
+.endm
+.macro PTGS_TO_GS_EX
+.endm
+.macro GS_TO_REG reg
+.endm
+.macro REG_TO_PTGS reg
+.endm
+.macro SET_KERNEL_GS reg
+.endm
+
+#else	/* CONFIG_X86_32_LAZY_GS */
+
+.macro PUSH_GS
+	pushl %gs
+	CFI_ADJUST_CFA_OFFSET 4
+	/*CFI_REL_OFFSET gs, 0*/
+.endm
+
+.macro POP_GS pop=0
+98:	popl %gs
+	CFI_ADJUST_CFA_OFFSET -4
+	/*CFI_RESTORE gs*/
+  .if \pop <> 0
+	add $\pop, %esp
+	CFI_ADJUST_CFA_OFFSET -\pop
+  .endif
+.endm
+.macro POP_GS_EX
+.pushsection .fixup, "ax"
+99:	movl $0, (%esp)
+	jmp 98b
+.section __ex_table, "a"
+	.align 4
+	.long 98b, 99b
+.popsection
+.endm
+
+.macro PTGS_TO_GS
+98:	mov PT_GS(%esp), %gs
+.endm
+.macro PTGS_TO_GS_EX
+.pushsection .fixup, "ax"
+99:	movl $0, PT_GS(%esp)
+	jmp 98b
+.section __ex_table, "a"
+	.align 4
+	.long 98b, 99b
+.popsection
+.endm
+
+.macro GS_TO_REG reg
+	movl %gs, \reg
+	/*CFI_REGISTER gs, \reg*/
+.endm
+.macro REG_TO_PTGS reg
+	movl \reg, PT_GS(%esp)
+	/*CFI_REL_OFFSET gs, PT_GS*/
+.endm
+.macro SET_KERNEL_GS reg
+	xorl \reg, \reg
+	movl \reg, %gs
+.endm
+
+#endif	/* CONFIG_X86_32_LAZY_GS */
+
 .macro SAVE_ALL
 	cld
+	PUSH_GS
 	pushl %fs
 	CFI_ADJUST_CFA_OFFSET 4
 	/*CFI_REL_OFFSET fs, 0;*/
@@ -138,6 +230,7 @@
 	movl %edx, %es
 	movl $(__KERNEL_PERCPU), %edx
 	movl %edx, %fs
+	SET_KERNEL_GS %edx
 .endm
 
 .macro RESTORE_INT_REGS
@@ -164,7 +257,7 @@
 	CFI_RESTORE eax
 .endm
 
-.macro RESTORE_REGS
+.macro RESTORE_REGS pop=0
 	RESTORE_INT_REGS
 1:	popl %ds
 	CFI_ADJUST_CFA_OFFSET -4
@@ -175,6 +268,7 @@
 3:	popl %fs
 	CFI_ADJUST_CFA_OFFSET -4
 	/*CFI_RESTORE fs;*/
+	POP_GS \pop
 .pushsection .fixup, "ax"
 4:	movl $0, (%esp)
 	jmp 1b
@@ -188,6 +282,7 @@
 	.long 2b, 5b
 	.long 3b, 6b
 .popsection
+	POP_GS_EX
 .endm
 
 .macro RING0_INT_FRAME
@@ -368,6 +463,7 @@ sysenter_exit:
 	xorl %ebp,%ebp
 	TRACE_IRQS_ON
 1:	mov  PT_FS(%esp), %fs
+	PTGS_TO_GS
 	ENABLE_INTERRUPTS_SYSEXIT
 
 #ifdef CONFIG_AUDITSYSCALL
@@ -416,6 +512,7 @@ sysexit_audit:
 	.align 4
 	.long 1b,2b
 .popsection
+	PTGS_TO_GS_EX
 ENDPROC(ia32_sysenter_target)
 
 	# system call handler stub
@@ -458,8 +555,7 @@ restore_all:
 restore_nocheck:
 	TRACE_IRQS_IRET
 restore_nocheck_notrace:
-	RESTORE_REGS
-	addl $4, %esp			# skip orig_eax/error_code
+	RESTORE_REGS 4			# skip orig_eax/error_code
 	CFI_ADJUST_CFA_OFFSET -4
 irq_return:
 	INTERRUPT_RETURN
@@ -1078,7 +1174,10 @@ ENTRY(page_fault)
 	CFI_ADJUST_CFA_OFFSET 4
 	ALIGN
 error_code:
-	/* the function address is in %fs's slot on the stack */
+	/* the function address is in %gs's slot on the stack */
+	pushl %fs
+	CFI_ADJUST_CFA_OFFSET 4
+	/*CFI_REL_OFFSET fs, 0*/
 	pushl %es
 	CFI_ADJUST_CFA_OFFSET 4
 	/*CFI_REL_OFFSET es, 0*/
@@ -1107,20 +1206,15 @@ error_code:
 	CFI_ADJUST_CFA_OFFSET 4
 	CFI_REL_OFFSET ebx, 0
 	cld
-	pushl %fs
-	CFI_ADJUST_CFA_OFFSET 4
-	/*CFI_REL_OFFSET fs, 0*/
 	movl $(__KERNEL_PERCPU), %ecx
 	movl %ecx, %fs
 	UNWIND_ESPFIX_STACK
-	popl %ecx
-	CFI_ADJUST_CFA_OFFSET -4
-	/*CFI_REGISTER es, ecx*/
-	movl PT_FS(%esp), %edi		# get the function address
+	GS_TO_REG %ecx
+	movl PT_GS(%esp), %edi		# get the function address
 	movl PT_ORIG_EAX(%esp), %edx	# get the error code
 	movl $-1, PT_ORIG_EAX(%esp)	# no syscall to restart
-	mov  %ecx, PT_FS(%esp)
-	/*CFI_REL_OFFSET fs, ES*/
+	REG_TO_PTGS %ecx
+	SET_KERNEL_GS %ecx
 	movl $(__USER_DS), %ecx
 	movl %ecx, %ds
 	movl %ecx, %es
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d58a340e1be3..86122fa2a1ba 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -539,7 +539,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	 * used %fs or %gs (it does not today), or if the kernel is
 	 * running inside of a hypervisor layer.
 	 */
-	savesegment(gs, prev->gs);
+	lazy_save_gs(prev->gs);
 
 	/*
 	 * Load the per-thread Thread-Local Storage descriptor.
@@ -585,7 +585,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	 * Restore %gs if needed (which is common)
 	 */
 	if (prev->gs | next->gs)
-		loadsegment(gs, next->gs);
+		lazy_load_gs(next->gs);
 
 	percpu_write(current_task, next_p);
 
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 508b6b57d0c3..7ec39ab37a2d 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -75,10 +75,7 @@ static inline bool invalid_selector(u16 value)
 static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long regno)
 {
 	BUILD_BUG_ON(offsetof(struct pt_regs, bx) != 0);
-	regno >>= 2;
-	if (regno > FS)
-		--regno;
-	return &regs->bx + regno;
+	return &regs->bx + (regno >> 2);
 }
 
 static u16 get_segment_reg(struct task_struct *task, unsigned long offset)