[Xen-devel] [PATCH v4 05/10] Clear AC bit in RFLAGS to protect Xen itself by SMAP

[Feng Wu <feng.wu@xxxxxxxxx>]

Clear AC bit in RFLAGS at the beginning of exception, interrupt, hypercall,
so Xen itself can be protected by SMAP mechanism.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
 xen/arch/x86/x86_64/compat/entry.S |  1 +
 xen/arch/x86/x86_64/entry.S        | 13 ++++++++-----
 xen/arch/x86/x86_64/traps.c        |  2 +-
 xen/include/asm-x86/asm_defns.h    |  5 ++++-
 4 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/x86_64/compat/entry.S 
b/xen/arch/x86/x86_64/compat/entry.S
index 32b3bcc..ac594c9 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -13,6 +13,7 @@
 #include <irq_vectors.h>
 
 ENTRY(compat_hypercall)
+        ASM_CLAC
         pushq $0
         SAVE_VOLATILE type=TRAP_syscall compat=1
 
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 1c81852..2b7072d 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -273,6 +273,7 @@ ENTRY(sysenter_entry)
         pushq $0
         pushfq
 GLOBAL(sysenter_eflags_saved)
+        ASM_CLAC
         pushq $3 /* ring 3 null cs */
         pushq $0 /* null rip */
         pushq $0
@@ -309,6 +310,7 @@ UNLIKELY_END(sysenter_gpf)
         jmp   .Lbounce_exception
 
 ENTRY(int80_direct_trap)
+        ASM_CLAC
         pushq $0
         SAVE_VOLATILE 0x80
 
@@ -466,7 +468,7 @@ ENTRY(dom_crash_sync_extable)
         jmp   asm_domain_crash_synchronous /* Does not return */
 
 ENTRY(common_interrupt)
-        SAVE_ALL
+        SAVE_ALL 1
         movq %rsp,%rdi
         callq do_IRQ
         jmp ret_from_intr
@@ -485,7 +487,7 @@ ENTRY(page_fault)
         movl  $TRAP_page_fault,4(%rsp)
 /* No special register assumptions. */
 GLOBAL(handle_exception)
-        SAVE_ALL
+        SAVE_ALL 1
 handle_exception_saved:
         testb $X86_EFLAGS_IF>>8,UREGS_eflags+1(%rsp)
         jz    exception_with_ints_disabled
@@ -614,7 +616,7 @@ ENTRY(spurious_interrupt_bug)
 
 ENTRY(double_fault)
         movl  $TRAP_double_fault,4(%rsp)
-        SAVE_ALL
+        SAVE_ALL 1
         movq  %rsp,%rdi
         call  do_double_fault
         ud2
@@ -631,7 +633,7 @@ ENTRY(nmi)
         pushq $0
         movl  $TRAP_nmi,4(%rsp)
 handle_ist_exception:
-        SAVE_ALL
+        SAVE_ALL 1
         testb $3,UREGS_cs(%rsp)
         jz    1f
         /* Interrupted guest context. Copy the context to stack bottom. */
@@ -667,12 +669,13 @@ handle_ist_exception:
 ENTRY(nmi_crash)
         pushq $0
         movl $TRAP_nmi,4(%rsp)
-        SAVE_ALL
+        SAVE_ALL 1
         movq %rsp,%rdi
         callq do_nmi_crash /* Does not return */
         ud2
 
 ENTRY(machine_check)
+        ASM_CLAC
         pushq $0
         movl  $TRAP_machine_check,4(%rsp)
         jmp   handle_ist_exception
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index 90072c1..b87b33e 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -437,7 +437,7 @@ void __devinit subarch_percpu_traps_init(void)
     /* Common SYSCALL parameters. */
     wrmsr(MSR_STAR, 0, (FLAT_RING3_CS32<<16) | __HYPERVISOR_CS);
     wrmsr(MSR_SYSCALL_MASK,
-          X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT|
+          X86_EFLAGS_AC|X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT|
           X86_EFLAGS_DF|X86_EFLAGS_IF|X86_EFLAGS_TF,
           0U);
 }
diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h
index 0eec635..df94dd5 100644
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -199,7 +199,10 @@ static inline void stac(void)
 #endif
 
 #ifdef __ASSEMBLY__
-.macro SAVE_ALL
+.macro SAVE_ALL clear_ac=0
+.if \clear_ac
+        ASM_CLAC
+.endif
         addq  $-(UREGS_error_code-UREGS_r15), %rsp
         cld
         movq  %rdi,UREGS_rdi(%rsp)
-- 
1.8.3.1


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