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 <Jason@zx2c4.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Fixes: 7e92e01b72452 ("powerpc: Provide syscall wrapper")
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221012035335.866440-1-npiggin@gmail.com

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index ee2d76cb3187..9b6146056e48 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -73,6 +73,7 @@ obj-y				:= cputable.o syscalls.o \
 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