[PATCH v1 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state

[Thomas Garnier]

Implement specific usage of verify_pre_usermode_state for user-mode
returns for x86.
---
Based on next-20170308
---
 arch/x86/Kconfig          | 1 +
 arch/x86/entry/common.c   | 3 +++
 arch/x86/entry/entry_64.S | 6 ++++++
 3 files changed, 10 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 005df7c825f5..6d48e18e6f09 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -63,6 +63,7 @@ config X86
        select ARCH_MIGHT_HAVE_ACPI_PDC         if ACPI
        select ARCH_MIGHT_HAVE_PC_PARPORT
        select ARCH_MIGHT_HAVE_PC_SERIO
+       select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
        select ARCH_SUPPORTS_ATOMIC_RMW
        select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
        select ARCH_SUPPORTS_NUMA_BALANCING     if X86_64
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 370c42c7f046..525edbb77f03 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -22,6 +22,7 @@
 #include <linux/context_tracking.h>
 #include <linux/user-return-notifier.h>
 #include <linux/uprobes.h>
+#include <linux/syscalls.h>
 
 #include <asm/desc.h>
 #include <asm/traps.h>
@@ -180,6 +181,8 @@ __visible inline void prepare_exit_to_usermode(struct 
pt_regs *regs)
        struct thread_info *ti = current_thread_info();
        u32 cached_flags;
 
+       verify_pre_usermode_state();
+
        if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
                local_irq_disable();
 
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d2b2a2948ffe..795c31eebd09 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -201,6 +201,7 @@ entry_SYSCALL_64_fastpath:
         * It might end up jumping to the slow path.  If it jumps, RAX
         * and all argument registers are clobbered.
         */
+
        call    *sys_call_table(, %rax, 8)
 .Lentry_SYSCALL_64_after_fastpath_call:
 
@@ -218,6 +219,11 @@ entry_SYSCALL_64_fastpath:
        testl   $_TIF_ALLWORK_MASK, TASK_TI_flags(%r11)
        jnz     1f
 
+       /*
+        * Check user-mode state on fast path return, the same check is done
+        * under the slow path through syscall_return_slowpath.
+        */
+       call    verify_pre_usermode_state
        LOCKDEP_SYS_EXIT
        TRACE_IRQS_ON           /* user mode is traced as IRQs on */
        movq    RIP(%rsp), %rcx
-- 
2.12.0.246.ga2ecc84866-goog