[RFC v2 -tip 1/3] x86: uaccess: introduce try and catch framework

Hiroshi Shimamoto
2009-01-23T23:49:50Z

From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>

Impact: introduce new uaccess exception handling framework

Introduce {get|put}_user_try and {get|put}_user_catch as new uaccess exception
handling framework.
{get|put}_user_try begins exception block and {get|put}_user_catch(err) ends
the block and gets err if an exception occured in {get|put}_user_ex() in the
block. The exception is stored thread_info->uaccess_err.

The example usage of this framework is below;
int func()
{
int err = 0;

get_user_try {
get_user_ex(...);
get_user_ex(...);
:
} get_user_catch(err);

return err;
}

Note: get_user_ex() is not clear the value when an exception occurs, it's
different from the behavior of __get_user(), but I think it doesn't matter.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
---
arch/x86/include/asm/thread_info.h | 1 +
arch/x86/include/asm/uaccess.h | 103 ++++++++++++++++++++++++++++++++++++
arch/x86/mm/extable.c | 6 ++
3 files changed, 110 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index f384889..ca7310e 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -40,6 +40,7 @@ struct thread_info {
*/
__u8 supervisor_stack[0];
#endif
+ int uaccess_err;
};

#define INIT_THREAD_INFO(tsk) \
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 69d2757..0ec6de4 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -199,12 +199,22 @@ extern int __get_user_bad(void);
: "=r" (err) \
: "A" (x), "r" (addr), "i" (-EFAULT), "0" (err))

+#define __put_user_asm_ex_u64(x, addr) \
+ asm volatile("1: movl %%eax,0(%1)\n" \
+ "2: movl %%edx,4(%1)\n" \
+ "3:\n" \
+ _ASM_EXTABLE(1b, 2b - 1b) \
+ _ASM_EXTABLE(2b, 3b - 2b) \
+ : : "A" (x), "r" (addr))
+
#define __put_user_x8(x, ptr, __ret_pu) \
asm volatile("call __put_user_8" : "=a" (__ret_pu) \
: "A" ((typeof(*(ptr)))(x)), "c" (ptr) : "ebx")
#else
#define __put_user_asm_u64(x, ptr, retval) \
__put_user_asm(x, ptr, retval, "q", "", "Zr", -EFAULT)
+#define __put_user_asm_ex_u64(x, addr) \
+ __put_user_asm_ex(x, addr, "q", "", "Zr")
#define __put_user_x8(x, ptr, __ret_pu) __put_user_x(8, x, ptr, __ret_pu)
#endif

@@ -286,6 +296,27 @@ do { \
} \
} while (0)

+#define __put_user_size_ex(x, ptr, size) \
+do { \
+ __chk_user_ptr(ptr); \
+ switch (size) { \
+ case 1: \
+ __put_user_asm_ex(x, ptr, "b", "b", "iq"); \
+ break; \
+ case 2: \
+ __put_user_asm_ex(x, ptr, "w", "w", "ir"); \
+ break; \
+ case 4: \
+ __put_user_asm_ex(x, ptr, "l", "k", "ir"); \
+ break; \
+ case 8: \
+ __put_user_asm_ex_u64((__typeof__(*ptr))(x), ptr); \
+ break; \
+ default: \
+ __put_user_bad(); \
+ } \
+} while (0)
+
#else

#define __put_user_size(x, ptr, size, retval, errret) \
@@ -311,9 +342,12 @@ do { \

#ifdef CONFIG_X86_32
#define __get_user_asm_u64(x, ptr, retval, errret) (x) = __get_user_bad()
+#define __get_user_asm_ex_u64(x, ptr) (x) = __get_user_bad()
#else
#define __get_user_asm_u64(x, ptr, retval, errret) \
__get_user_asm(x, ptr, retval, "q", "", "=r", errret)
+#define __get_user_asm_ex_u64(x, ptr) \
+ __get_user_asm_ex(x, ptr, "q", "", "=r")
#endif

#define __get_user_size(x, ptr, size, retval, errret) \
@@ -350,6 +384,33 @@ do { \
: "=r" (err), ltype(x) \
: "m" (__m(addr)), "i" (errret), "0" (err))

+#define __get_user_size_ex(x, ptr, size) \
+do { \
+ __chk_user_ptr(ptr); \
+ switch (size) { \
+ case 1: \
+ __get_user_asm_ex(x, ptr, "b", "b", "=q"); \
+ break; \
+ case 2: \
+ __get_user_asm_ex(x, ptr, "w", "w", "=r"); \
+ break; \
+ case 4: \
+ __get_user_asm_ex(x, ptr, "l", "k", "=r"); \
+ break; \
+ case 8: \
+ __get_user_asm_ex_u64(x, ptr); \
+ break; \
+ default: \
+ (x) = __get_user_bad(); \
+ } \
+} while (0)
+
+#define __get_user_asm_ex(x, addr, itype, rtype, ltype) \
+ asm volatile("1: mov"itype" %1,%"rtype"0\n" \
+ "2:\n" \
+ _ASM_EXTABLE(1b, 2b - 1b) \
+ : ltype(x) : "m" (__m(addr)))
+
#define __put_user_nocheck(x, ptr, size) \
({ \
int __pu_err; \
@@ -385,6 +446,26 @@ struct __large_struct { unsigned long buf[100]; };
_ASM_EXTABLE(1b, 3b) \
: "=r"(err) \
: ltype(x), "m" (__m(addr)), "i" (errret), "0" (err))
+
+#define __put_user_asm_ex(x, addr, itype, rtype, ltype) \
+ asm volatile("1: mov"itype" %"rtype"0,%1\n" \
+ "2:\n" \
+ _ASM_EXTABLE(1b, 2b - 1b) \
+ : : ltype(x), "m" (__m(addr)))
+
+/*
+ * uaccess_try and catch
+ */
+#define uaccess_try do { \
+ int prev_err = current_thread_info()->uaccess_err; \
+ current_thread_info()->uaccess_err = 0; \
+ barrier();
+
+#define uaccess_catch(err) \
+ (err) |= current_thread_info()->uaccess_err; \
+ current_thread_info()->uaccess_err = prev_err; \
+} while (0)
+
/**
* __get_user: - Get a simple variable from user space, with less checking.
* @x: Variable to store result.
@@ -408,6 +489,7 @@ struct __large_struct { unsigned long buf[100]; };

#define __get_user(x, ptr) \
__get_user_nocheck((x), (ptr), sizeof(*(ptr)))
+
/**
* __put_user: - Write a simple value into user space, with less checking.
* @x: Value to copy to user space.
@@ -435,6 +517,27 @@ struct __large_struct { unsigned long buf[100]; };
#define __put_user_unaligned __put_user

/*
+ * {get|put}_user_try and catch
+ *
+ * get_user_try {
+ * get_user_ex(...);
+ * } get_user_catch(err)
+ */
+#define get_user_try uaccess_try
+#define get_user_catch(err) uaccess_catch(err)
+#define put_user_try uaccess_try
+#define put_user_catch(err) uaccess_catch(err)
+
+#define get_user_ex(x, ptr) do { \
+ unsigned long __gue_val; \
+ __get_user_size_ex((__gue_val), (ptr), (sizeof(*(ptr)))); \
+ (x) = (__force __typeof__(*(ptr)))__gue_val; \
+} while (0)
+
+#define put_user_ex(x, ptr) \
+ __put_user_size_ex((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
+
+/*
* movsl can be slow when source and dest are not both 8-byte aligned
*/
#ifdef CONFIG_X86_INTEL_USERCOPY
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 7e8db53..61b41ca 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -23,6 +23,12 @@ int fixup_exception(struct pt_regs *regs)

fixup = search_exception_tables(regs->ip);
if (fixup) {
+ /* If fixup is less than 16, it means uaccess error */
+ if (fixup->fixup < 16) {
+ current_thread_info()->uaccess_err = -EFAULT;
+ regs->ip += fixup->fixup;
+ return 1;
+ }
regs->ip = fixup->fixup;
return 1;
}
--
1.6.0.4