Re: [PATCH] Expose range-checking functions from arch-specificuaccess.h
From: Rusty Russell
Date: Wed Apr 04 2007 - 02:42:04 EST
On Tue, 2007-04-03 at 20:22 -0700, Randy Dunlap wrote:
> > +/**
> > + * val_outside - is a value and length past a limit?
> > + * @val: the start value
> > + * @len: the length from the start
> > + * @limit: the first invalid value
> > + *
> > + * Like val + len > limit, except with overflow checking.
> > + */
> > +static inline bool val_outside(unsigned long val, unsigned long len,
> > + unsigned long limit)
> > +
> > +{
> > + return val + len > limit || val + len < val;
>
> why isn't that
> return val + len >= limit || val + len < val;
Hi Randy!
Good question! Mainly because that's what the existing __range_ok()
function does: limit is the first *invalid* value, not the last valid
value.
Say your limit is 0xC000 0000. You want to be able to write 1 byte to
0xBFFF FFFF. So it's only outside if val + len > limit.
> > +#define __range_ok(addr,size) ({ \
> > + __chk_user_ptr(addr); \
> > + val_outside((int)(addr),(size),current_thread_info()->addr_limit.seg); \
>
> space after commas, please.
Yeah, I copied the existing code (but gladly: spaces pushes us onto
another line). Fixed.
> > + * This is usually used for memory range testing. The common cases of
> > + * constant 0 start and constant 0 len cases are optimized out.
> > + */
>
> Where is constant 0 start optimized out?
The start < base is optimized out if base is known to be 0 (they're both
unsigned): gcc realizes that can never be true so kills that whole
branch.
> > +static inline bool range_within(unsigned long start, unsigned long len,
> > + unsigned long base, unsigned long limit)
> > +{
> > + if (start < base)
> > + return false;
> > + if (__builtin_constant_p(len) && len == 0)
>
> I don't see what the builtin_constant_p() adds here.
> If len == 0, this return <expression> is still OK, isn't it?
We don't really want a branch in this code: __builtin_constant_p()
ensures we end up only with "start - base <= limit - base" or "!
val_outside(limit, start, len)" in the binary.
> > diff -r 4272a6d4f27c include/asm-arm/range.h
> > --- /dev/null Thu Jan 01 00:00:00 1970 +0000
> > +++ b/include/asm-arm/range.h Wed Apr 04 12:14:45 2007 +1000
> > @@ -0,0 +1,6 @@
> > +#ifndef __ALPHA_RANGE_H
> > +#define __ALPHA_RANGE_H
>
> why ALPHA ?
Oops. Because I coded this with a "for d in include/asm-*...".
Fixed.
Thanks!
Rusty.
==
There are some places where we want to check if a value + length is
within a range. This can be tricky, so it's nice to have a single
routine.
Also, this can be done more efficiently (with arch-dependent) carry
bits, as shown by the __range_ok() implementation on several archs.
This patch exposes arch-specific "val_outside(val, len, limit)" and a
generic "range_within(start, len, base, limit)" function. As a
side-effect, it fixes the comment in i386/uaccess.h: __range_ok
doesn't test "(u33)addr + (u33)size >= (u33)current->addr_limit.seg",
it tests "(u33)addr + (u33)size > (u33)current->addr_limit.seg".
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff -r 4815a24d0254 include/linux/kernel.h
--- a/include/linux/kernel.h Wed Apr 04 16:35:57 2007 +1000
+++ b/include/linux/kernel.h Wed Apr 04 16:36:00 2007 +1000
@@ -16,6 +16,7 @@
#include <linux/log2.h>
#include <asm/byteorder.h>
#include <asm/bug.h>
+#include <asm/range.h>
extern const char linux_banner[];
extern const char linux_proc_banner[];
@@ -311,6 +312,26 @@ static inline int __attribute__ ((format
(void)__tmp; \
})
+/**
+ * range_within - is one range within another?
+ * @start: the start value
+ * @len: the length from the start
+ * @base: the first valid value
+ * @limit: the first invalid value
+ *
+ * This is usually used for memory range testing. The common cases of
+ * constant 0 start and constant 0 len cases are optimized out.
+ */
+static inline bool range_within(unsigned long start, unsigned long len,
+ unsigned long base, unsigned long limit)
+{
+ if (start < base)
+ return false;
+ if (__builtin_constant_p(len) && len == 0)
+ return start - base <= limit - base;
+ return !val_outside(limit, start, len);
+}
+
struct sysinfo;
extern int do_sysinfo(struct sysinfo *info);
diff -r 4815a24d0254 include/asm-i386/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-i386/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,14 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+/* Is val + size > limit? This needs 33-bit arithmetic. We have a carry... */
+static inline bool val_outside(unsigned long val, unsigned long len,
+ unsigned long limit)
+{
+ unsigned long flag, roksum;
+ asm("addl %3,%1 ; sbbl %0,%0; cmpl %1,%4; sbbl $0,%0"
+ :"=&r" (flag), "=r" (roksum)
+ :"1" (val), "g" (len), "rm" (limit));
+ return flag;
+}
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-i386/uaccess.h
--- a/include/asm-i386/uaccess.h Wed Apr 04 16:35:57 2007 +1000
+++ b/include/asm-i386/uaccess.h Wed Apr 04 16:36:34 2007 +1000
@@ -49,17 +49,13 @@ extern struct movsl_mask {
* Returns 0 if the range is valid, nonzero otherwise.
*
* This is equivalent to the following test:
- * (u33)addr + (u33)size >= (u33)current->addr_limit.seg
- *
- * This needs 33-bit arithmetic. We have a carry...
- */
-#define __range_ok(addr,size) ({ \
- unsigned long flag,roksum; \
- __chk_user_ptr(addr); \
- asm("addl %3,%1 ; sbbl %0,%0; cmpl %1,%4; sbbl $0,%0" \
- :"=&r" (flag), "=r" (roksum) \
- :"1" (addr),"g" ((int)(size)),"rm" (current_thread_info()->addr_limit.seg)); \
- flag; })
+ * (u33)addr + (u33)size > (u33)current->addr_limit.seg
+ */
+#define __range_ok(addr, size) ({ \
+ __chk_user_ptr(addr); \
+ val_outside((int)(addr), (size), \
+ current_thread_info()->addr_limit.seg); \
+})
/**
* access_ok: - Checks if a user space pointer is valid
diff -r 4815a24d0254 include/asm-generic/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-generic/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,20 @@
+#ifndef _ASM_GENERIC_RANGE_H
+#define _ASM_GENERIC_RANGE_H
+
+/**
+ * val_outside - is a value and length past a limit?
+ * @val: the start value
+ * @len: the length from the start
+ * @limit: the first invalid value
+ *
+ * Like val + len > limit, except with overflow checking.
+ */
+static inline bool val_outside(unsigned long val, unsigned long len,
+ unsigned long limit)
+
+{
+ return val + len > limit || val + len < val;
+}
+
+#endif /* _ASM_GENERIC_RANGE_H */
+
diff -r 4815a24d0254 include/asm-alpha/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-alpha/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-arm/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-arm/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-arm26/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-arm26/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-avr32/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-avr32/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-blackfin/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-blackfin/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-cris/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-cris/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-frv/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-frv/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-h8300/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-h8300/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-ia64/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-ia64/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-m32r/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-m32r/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-m68k/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-m68k/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-m68knommu/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-m68knommu/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-mips/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-mips/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-parisc/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-parisc/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-powerpc/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-powerpc/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-ppc/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-ppc/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-s390/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-s390/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-sh/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-sh/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-sh64/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-sh64/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-sparc/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-sparc/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-sparc64/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-sparc64/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-um/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-um/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-v850/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-v850/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-x86_64/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-x86_64/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
diff -r 4815a24d0254 include/asm-xtensa/range.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/include/asm-xtensa/range.h Wed Apr 04 16:36:00 2007 +1000
@@ -0,0 +1,6 @@
+#ifndef __ASM_RANGE_H
+#define __ASM_RANGE_H
+
+#include <asm-generic/range.h>
+
+#endif /* __ASM_RANGE_H */
-
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