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>
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 39b0aac..83c1bc8 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -112,7 +112,7 @@
* now struct_user_regs, they are different)
*/
-#define ELF_CORE_COPY_REGS(pr_reg, regs) \
+#define ELF_CORE_COPY_REGS_COMMON(pr_reg, regs) \
do { \
pr_reg[0] = regs->bx; \
pr_reg[1] = regs->cx; \
@@ -124,7 +124,6 @@
pr_reg[7] = regs->ds & 0xffff; \
pr_reg[8] = regs->es & 0xffff; \
pr_reg[9] = regs->fs & 0xffff; \
- pr_reg[10] = get_user_gs(regs); \
pr_reg[11] = regs->orig_ax; \
pr_reg[12] = regs->ip; \
pr_reg[13] = regs->cs & 0xffff; \
@@ -133,6 +132,18 @@
pr_reg[16] = regs->ss & 0xffff; \
} while (0);
+#define ELF_CORE_COPY_REGS(pr_reg, regs) \
+do { \
+ ELF_CORE_COPY_REGS_COMMON(pr_reg, regs);\
+ pr_reg[10] = get_user_gs(regs); \
+} while (0);
+
+#define ELF_CORE_COPY_KERNEL_REGS(pr_reg, regs) \
+do { \
+ ELF_CORE_COPY_REGS_COMMON(pr_reg, regs);\
+ savesegment(gs, pr_reg[10]); \
+} while (0);
+
#define ELF_PLATFORM (utsname()->machine)
#define set_personality_64bit() do { } while (0)
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 4955165..f923203 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -79,7 +79,7 @@
#ifdef CONFIG_X86_32
#define deactivate_mm(tsk, mm) \
do { \
- set_user_gs(task_pt_regs(tsk), 0); \
+ lazy_load_gs(0); \
} while (0)
#else
#define deactivate_mm(tsk, mm) \
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 6d34d95..e304b66 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -28,7 +28,7 @@
int xds;
int xes;
int xfs;
- /* int gs; */
+ int xgs;
long orig_eax;
long eip;
int xcs;
@@ -50,7 +50,7 @@
unsigned long ds;
unsigned long es;
unsigned long fs;
- /* int gs; */
+ unsigned long gs;
unsigned long orig_ax;
unsigned long ip;
unsigned long cs;
diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index 70c74b8..79b98e5 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -186,10 +186,20 @@
* x86_32 user gs accessors.
*/
#ifdef CONFIG_X86_32
+#ifdef CONFIG_X86_32_LAZY_GS
#define get_user_gs(regs) (u16)({unsigned long v; savesegment(gs, v); v;})
#define set_user_gs(regs, v) loadsegment(gs, (unsigned long)(v))
#define task_user_gs(tsk) ((tsk)->thread.gs)
-#endif
+#define lazy_save_gs(v) savesegment(gs, (v))
+#define lazy_load_gs(v) loadsegment(gs, (v))
+#else /* X86_32_LAZY_GS */
+#define get_user_gs(regs) (u16)((regs)->gs)
+#define set_user_gs(regs, v) do { (regs)->gs = (v); } while (0)
+#define task_user_gs(tsk) (task_pt_regs(tsk)->gs)
+#define lazy_save_gs(v) do { } while (0)
+#define lazy_load_gs(v) do { } while (0)
+#endif /* X86_32_LAZY_GS */
+#endif /* X86_32 */
static inline unsigned long get_limit(unsigned long segment)
{