powerpc/compat_sys: swap hi/lo parts of 64-bit syscall args in LE mode

Swap upper/lower 32 bits for 64-bit compat syscalls, conditioned on
endianness. This is modeled after the same functionality in
arch/mips/kernel/linux32.c.

This fixes compat_sys on ppc64le, when called by 32-bit little-endian
processes.

Tested with `file /bin/bash` (pread64) and `truncate -s 5G test`
(ftruncate64).
Signed-off-by: Will Springer <skirmisher@protonmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2765111.e9J7NaK4W3@sheen

arch/powerpc/kernel/sys_ppc32.c

@@ -59,57 +59,64 @@ unsigned long compat_sys_mmap2(unsigned long addr, size_t len,
 /* 
  * long long munging:
  * The 32 bit ABI passes long longs in an odd even register pair.
+ * High and low parts are swapped depending on endian mode,
+ * so define a macro (similar to mips linux32) to handle that.
  */
+#ifdef __LITTLE_ENDIAN__
+#define merge_64(low, high) ((u64)high << 32) | low
+#else
+#define merge_64(high, low) ((u64)high << 32) | low
+#endif
 
 compat_ssize_t compat_sys_pread64(unsigned int fd, char __user *ubuf, compat_size_t count,
-			     u32 reg6, u32 poshi, u32 poslo)
+			     u32 reg6, u32 pos1, u32 pos2)
 {
-	return ksys_pread64(fd, ubuf, count, ((loff_t)poshi << 32) | poslo);
+	return ksys_pread64(fd, ubuf, count, merge_64(pos1, pos2));
 }
 
 compat_ssize_t compat_sys_pwrite64(unsigned int fd, const char __user *ubuf, compat_size_t count,
-			      u32 reg6, u32 poshi, u32 poslo)
+			      u32 reg6, u32 pos1, u32 pos2)
 {
-	return ksys_pwrite64(fd, ubuf, count, ((loff_t)poshi << 32) | poslo);
+	return ksys_pwrite64(fd, ubuf, count, merge_64(pos1, pos2));
 }
 
-compat_ssize_t compat_sys_readahead(int fd, u32 r4, u32 offhi, u32 offlo, u32 count)
+compat_ssize_t compat_sys_readahead(int fd, u32 r4, u32 offset1, u32 offset2, u32 count)
 {
-	return ksys_readahead(fd, ((loff_t)offhi << 32) | offlo, count);
+	return ksys_readahead(fd, merge_64(offset1, offset2), count);
 }
 
 asmlinkage int compat_sys_truncate64(const char __user * path, u32 reg4,
-				unsigned long high, unsigned long low)
+				unsigned long len1, unsigned long len2)
 {
-	return ksys_truncate(path, (high << 32) | low);
+	return ksys_truncate(path, merge_64(len1, len2));
 }
 
-asmlinkage long compat_sys_fallocate(int fd, int mode, u32 offhi, u32 offlo,
-				     u32 lenhi, u32 lenlo)
+asmlinkage long compat_sys_fallocate(int fd, int mode, u32 offset1, u32 offset2,
+				     u32 len1, u32 len2)
 {
-	return ksys_fallocate(fd, mode, ((loff_t)offhi << 32) | offlo,
-			     ((loff_t)lenhi << 32) | lenlo);
+	return ksys_fallocate(fd, mode, ((loff_t)offset1 << 32) | offset2,
+			     merge_64(len1, len2));
 }
 
-asmlinkage int compat_sys_ftruncate64(unsigned int fd, u32 reg4, unsigned long high,
-				 unsigned long low)
+asmlinkage int compat_sys_ftruncate64(unsigned int fd, u32 reg4, unsigned long len1,
+				 unsigned long len2)
 {
-	return ksys_ftruncate(fd, (high << 32) | low);
+	return ksys_ftruncate(fd, merge_64(len1, len2));
 }
 
-long ppc32_fadvise64(int fd, u32 unused, u32 offset_high, u32 offset_low,
+long ppc32_fadvise64(int fd, u32 unused, u32 offset1, u32 offset2,
 		     size_t len, int advice)
 {
-	return ksys_fadvise64_64(fd, (u64)offset_high << 32 | offset_low, len,
+	return ksys_fadvise64_64(fd, merge_64(offset1, offset2), len,
 				 advice);
 }
 
 asmlinkage long compat_sys_sync_file_range2(int fd, unsigned int flags,
-				   unsigned offset_hi, unsigned offset_lo,
-				   unsigned nbytes_hi, unsigned nbytes_lo)
+				   unsigned offset1, unsigned offset2,
+				   unsigned nbytes1, unsigned nbytes2)
 {
-	loff_t offset = ((loff_t)offset_hi << 32) | offset_lo;
-	loff_t nbytes = ((loff_t)nbytes_hi << 32) | nbytes_lo;
+	loff_t offset = merge_64(offset1, offset2);
+	loff_t nbytes = merge_64(nbytes1, nbytes2);
 
 	return ksys_sync_file_range(fd, offset, nbytes, flags);
 }