powerpc/32: fix syscall wrappers with 64-bit arguments of unaligned register-pairs

powerpc 32-bit system call (and function) calling convention for 64-bit
arguments requires the next available odd-pair (two sequential registers
with the first being odd-numbered) from the standard register argument
allocation.

The first argument register is r3, so a 64-bit argument that appears at
an even position in the argument list must skip a register (unless there
were preceding 64-bit arguments, which might throw things off). This
requires non-standard compat definitions to deal with the holes in the
argument register allocation.

With pt_regs syscall wrappers which use a standard mapper to map pt_regs
GPRs to function arguments, 32-bit kernels hit the same basic problem,
the standard definitions don't cope with the unused argument registers.

Fix this by having 32-bit kernels share those syscall definitions with
compat.

Thanks to Jason for spending a lot of time finding and bisecting this
and developing a trivial reproducer. The perfect bug report.

Reported-by: Jason A. Donenfeld <[e-mail]>
Signed-off-by: Nicholas Piggin <[e-mail]>
Fixes: 7e92e01b72452 ("powerpc: Provide syscall wrapper")
Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/include/asm/syscalls.h

···
  * responsible for combining parameter pairs.
  */
 
+#ifdef CONFIG_PPC32
+long sys_ppc_pread64(unsigned int fd,
+		     char __user *ubuf, compat_size_t count,
+		     u32 reg6, u32 pos1, u32 pos2);
+long sys_ppc_pwrite64(unsigned int fd,
+		      const char __user *ubuf, compat_size_t count,
+		      u32 reg6, u32 pos1, u32 pos2);
+long sys_ppc_readahead(int fd, u32 r4,
+		       u32 offset1, u32 offset2, u32 count);
+long sys_ppc_truncate64(const char __user *path, u32 reg4,
+		        unsigned long len1, unsigned long len2);
+long sys_ppc_ftruncate64(unsigned int fd, u32 reg4,
+			 unsigned long len1, unsigned long len2);
+long sys_ppc32_fadvise64(int fd, u32 unused, u32 offset1, u32 offset2,
+			 size_t len, int advice);
+#endif
 #ifdef CONFIG_COMPAT
 long compat_sys_mmap2(unsigned long addr, size_t len,
 		      unsigned long prot, unsigned long flags,

arch/powerpc/kernel/Makefile

···
 obj-y				+= ptrace/
 obj-$(CONFIG_PPC64)		+= setup_64.o irq_64.o\
 				   paca.o nvram_64.o note.o
+obj-$(CONFIG_PPC32)		+= sys_ppc32.o
 obj-$(CONFIG_COMPAT)		+= sys_ppc32.o signal_32.o
 obj-$(CONFIG_VDSO32)		+= vdso32_wrapper.o
 obj-$(CONFIG_PPC_WATCHDOG)	+= watchdog.o

arch/powerpc/kernel/sys_ppc32.c

···
 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
- * sys_ppc32.c: Conversion between 32bit and 64bit native syscalls.
+ * sys_ppc32.c: 32-bit system calls with complex calling conventions.
  *
  * Copyright (C) 2001 IBM
  * Copyright (C) 1997,1998 Jakub Jelinek ([e-mail])
  * Copyright (C) 1997 David S. Miller ([e-mail])
  *
- * These routines maintain argument size conversion between 32bit and 64bit
- * environment.
+ * 32-bit system calls with 64-bit arguments pass those in register pairs.
+ * This must be specially dealt with on 64-bit kernels. The compat_arg_u64_dual
+ * in generic compat syscalls is not always usable because the register
+ * pairing is constrained depending on preceding arguments.
+ *
+ * An analogous problem exists on 32-bit kernels with ARCH_HAS_SYSCALL_WRAPPER,
+ * the defined system call functions take the pt_regs as an argument, and there
+ * is a mapping macro which maps registers to arguments
+ * (SC_POWERPC_REGS_TO_ARGS) which also does not deal with these 64-bit
+ * arguments.
+ *
+ * This file contains these system calls.
  */
 
 #include <linux/kernel.h>
···
 #include <asm/syscalls.h>
 #include <asm/switch_to.h>
 
-COMPAT_SYSCALL_DEFINE6(ppc_pread64,
+#ifdef CONFIG_PPC32
+#define PPC32_SYSCALL_DEFINE4	SYSCALL_DEFINE4
+#define PPC32_SYSCALL_DEFINE5	SYSCALL_DEFINE5
+#define PPC32_SYSCALL_DEFINE6	SYSCALL_DEFINE6
+#else
+#define PPC32_SYSCALL_DEFINE4	COMPAT_SYSCALL_DEFINE4
+#define PPC32_SYSCALL_DEFINE5	COMPAT_SYSCALL_DEFINE5
+#define PPC32_SYSCALL_DEFINE6	COMPAT_SYSCALL_DEFINE6
+#endif
+
+PPC32_SYSCALL_DEFINE6(ppc_pread64,
 		       unsigned int, fd,
 		       char __user *, ubuf, compat_size_t, count,
 		       u32, reg6, u32, pos1, u32, pos2)
···
 	return ksys_pread64(fd, ubuf, count, merge_64(pos1, pos2));
 }
 
-COMPAT_SYSCALL_DEFINE6(ppc_pwrite64,
+PPC32_SYSCALL_DEFINE6(ppc_pwrite64,
 		       unsigned int, fd,
 		       const char __user *, ubuf, compat_size_t, count,
 		       u32, reg6, u32, pos1, u32, pos2)
···
 	return ksys_pwrite64(fd, ubuf, count, merge_64(pos1, pos2));
 }
 
-COMPAT_SYSCALL_DEFINE5(ppc_readahead,
+PPC32_SYSCALL_DEFINE5(ppc_readahead,
 		       int, fd, u32, r4,
 		       u32, offset1, u32, offset2, u32, count)
 {
 	return ksys_readahead(fd, merge_64(offset1, offset2), count);
 }
 
-COMPAT_SYSCALL_DEFINE4(ppc_truncate64,
+PPC32_SYSCALL_DEFINE4(ppc_truncate64,
 		       const char __user *, path, u32, reg4,
 		       unsigned long, len1, unsigned long, len2)
 {
 	return ksys_truncate(path, merge_64(len1, len2));
 }
 
-COMPAT_SYSCALL_DEFINE4(ppc_ftruncate64,
+PPC32_SYSCALL_DEFINE4(ppc_ftruncate64,
 		       unsigned int, fd, u32, reg4,
 		       unsigned long, len1, unsigned long, len2)
 {
 	return ksys_ftruncate(fd, merge_64(len1, len2));
 }
 
-COMPAT_SYSCALL_DEFINE6(ppc32_fadvise64,
+PPC32_SYSCALL_DEFINE6(ppc32_fadvise64,
 		       int, fd, u32, unused, u32, offset1, u32, offset2,
 		       size_t, len, int, advice)
 {

arch/powerpc/kernel/syscalls/syscall.tbl

···
 176	64	rt_sigtimedwait			sys_rt_sigtimedwait
 177	nospu 	rt_sigqueueinfo			sys_rt_sigqueueinfo		compat_sys_rt_sigqueueinfo
 178	nospu 	rt_sigsuspend			sys_rt_sigsuspend		compat_sys_rt_sigsuspend
-179	common	pread64				sys_pread64			compat_sys_ppc_pread64
-180	common	pwrite64			sys_pwrite64			compat_sys_ppc_pwrite64
+179	32	pread64				sys_ppc_pread64			compat_sys_ppc_pread64
+179	64	pread64				sys_pread64
+180	32	pwrite64			sys_ppc_pwrite64		compat_sys_ppc_pwrite64
+180	64	pwrite64			sys_pwrite64
 181	common	chown				sys_chown
 182	common	getcwd				sys_getcwd
 183	common	capget				sys_capget
···
 188	common 	putpmsg				sys_ni_syscall
 189	nospu	vfork				sys_vfork
 190	common	ugetrlimit			sys_getrlimit			compat_sys_getrlimit
-191	common	readahead			sys_readahead			compat_sys_ppc_readahead
+191	32	readahead			sys_ppc_readahead		compat_sys_ppc_readahead
+191	64	readahead			sys_readahead
 192	32	mmap2				sys_mmap2			compat_sys_mmap2
-193	32	truncate64			sys_truncate64			compat_sys_ppc_truncate64
-194	32	ftruncate64			sys_ftruncate64			compat_sys_ppc_ftruncate64
+193	32	truncate64			sys_ppc_truncate64		compat_sys_ppc_truncate64
+194	32	ftruncate64			sys_ppc_ftruncate64		compat_sys_ppc_ftruncate64
 195	32	stat64				sys_stat64
 196	32	lstat64				sys_lstat64
 197	32	fstat64				sys_fstat64
···
 230	common	io_submit			sys_io_submit			compat_sys_io_submit
 231	common	io_cancel			sys_io_cancel
 232	nospu	set_tid_address			sys_set_tid_address
-233	common	fadvise64			sys_fadvise64			compat_sys_ppc32_fadvise64
+233	32	fadvise64			sys_ppc32_fadvise64		compat_sys_ppc32_fadvise64
+233	64	fadvise64			sys_fadvise64
 234	nospu	exit_group			sys_exit_group
 235	nospu	lookup_dcookie			sys_lookup_dcookie		compat_sys_lookup_dcookie
 236	common	epoll_create			sys_epoll_create