aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/kernel
diff options
context:
space:
mode:
authorTejun Heo <tj@kernel.org>2009-02-09 22:17:40 +0900
committerIngo Molnar <mingo@elte.hu>2009-02-10 00:42:00 +0100
commitccbeed3a05908d201b47b6c3dd1a373138bba566 (patch)
treee834d548c70426aa3885dd2169be1a79be4a617b /arch/x86/kernel
parentd9a89a26e02ef9ed03f74a755a8b4d8f3a066622 (diff)
downloadlinux-ccbeed3a05908d201b47b6c3dd1a373138bba566.tar.gz
x86: make lazy %gs optional on x86_32
Impact: pt_regs changed, lazy gs handling made optional, add slight overhead to SAVE_ALL, simplifies error_code path a bit On x86_32, %gs hasn't been used by kernel and handled lazily. pt_regs doesn't have place for it and gs is saved/loaded only when necessary. In preparation for stack protector support, this patch makes lazy %gs handling optional by doing the followings. * Add CONFIG_X86_32_LAZY_GS and place for gs in pt_regs. * Save and restore %gs along with other registers in entry_32.S unless LAZY_GS. Note that this unfortunately adds "pushl $0" on SAVE_ALL even when LAZY_GS. However, it adds no overhead to common exit path and simplifies entry path with error code. * Define different user_gs accessors depending on LAZY_GS and add lazy_save_gs() and lazy_load_gs() which are noop if !LAZY_GS. The lazy_*_gs() ops are used to save, load and clear %gs lazily. * Define ELF_CORE_COPY_KERNEL_REGS() which always read %gs directly. xen and lguest changes need to be verified. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r--arch/x86/kernel/asm-offsets_32.c1
-rw-r--r--arch/x86/kernel/entry_32.S132
-rw-r--r--arch/x86/kernel/process_32.c4
-rw-r--r--arch/x86/kernel/ptrace.c5
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)