tile: work around bug in the generic sys_llseek

sys_llseek should specify the high and low 32-bit seek values as "unsigned
int" but instead it specifies "unsigned long".  Since compat syscall
arguments are always sign-extended on tile, this means that a seek value
of 0xffffffff will be incorrectly interpreted as a value of -1ULL.

To avoid the risk of breaking binary compatibility on architectures
that already use sys_llseek this way, we follow the same path as MIPS
and provide a wrapper override.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Cc: stable@kernel.org [v3.6 onwards]

arch/tile/include/asm/compat.h

@@ -288,6 +288,9 @@ long compat_sys_sync_file_range2(int fd, unsigned int flags,
 long compat_sys_fallocate(int fd, int mode,
 			  u32 offset_lo, u32 offset_hi,
 			  u32 len_lo, u32 len_hi);
+long compat_sys_llseek(unsigned int fd, unsigned int offset_high,
+		       unsigned int offset_low, loff_t __user * result,
+		       unsigned int origin);
 
 /* Assembly trampoline to avoid clobbering r0. */
 long _compat_sys_rt_sigreturn(void);

arch/tile/kernel/compat.c

@@ -76,13 +76,26 @@ long compat_sys_fallocate(int fd, int mode,
 			     ((loff_t)len_hi << 32) | len_lo);
 }
 
+/*
+ * Avoid bug in generic sys_llseek() that specifies offset_high and
+ * offset_low as "unsigned long", thus making it possible to pass
+ * a sign-extended high 32 bits in offset_low.
+ */
+long compat_sys_llseek(unsigned int fd, unsigned int offset_high,
+		       unsigned int offset_low, loff_t __user * result,
+		       unsigned int origin)
+{
+	return sys_llseek(fd, offset_high, offset_low, result, origin);
+}
+
 /* Provide the compat syscall number to call mapping. */
 #undef __SYSCALL
 #define __SYSCALL(nr, call) [nr] = (call),
 
 /* See comments in sys.c */
 #define compat_sys_fadvise64_64 sys32_fadvise64_64
 #define compat_sys_readahead sys32_readahead
+#define sys_llseek compat_sys_llseek
 
 /* Call the assembly trampolines where necessary. */
 #define compat_sys_rt_sigreturn _compat_sys_rt_sigreturn