[PATCH 5.12 109/292] s390/mem_detect: fix tprot() program check new psw handling

Greg Kroah-Hartman
2021-07-19T18:02:53Z

From: Heiko Carstens <hca@linux.ibm.com>

[ Upstream commit da9057576785aaab52e706e76c0475c85b77ec14 ]

The tprot() inline asm temporarily changes the program check new psw
to redirect a potential program check on the diag instruction.
Restoring of the program check new psw is done in C code behind the
inline asm.

This can be problematic, especially if the function is inlined, since
the compiler can reorder instructions in such a way that a different
instruction, which may result in a program check, might be executed
before the program check new psw has been restored.

To avoid such a scenario move restoring into the inline asm. For
consistency reasons move also saving of the original program check new
psw into the inline asm.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/boot/mem_detect.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/arch/s390/boot/mem_detect.c b/arch/s390/boot/mem_detect.c
index 3f093556dc3b..a0e980f57c02 100644
--- a/arch/s390/boot/mem_detect.c
+++ b/arch/s390/boot/mem_detect.c
@@ -114,24 +114,30 @@ static int diag260(void)

static int tprot(unsigned long addr)
{
- unsigned long pgm_addr;
+ unsigned long reg1, reg2;
int rc = -EFAULT;
- psw_t old = S390_lowcore.program_new_psw;
+ psw_t old;

- S390_lowcore.program_new_psw.mask = __extract_psw();
asm volatile(
- " larl %[pgm_addr],1f\n"
- " stg %[pgm_addr],%[psw_pgm_addr]\n"
+ " mvc 0(16,%[psw_old]),0(%[psw_pgm])\n"
+ " epsw %[reg1],%[reg2]\n"
+ " st %[reg1],0(%[psw_pgm])\n"
+ " st %[reg2],4(%[psw_pgm])\n"
+ " larl %[reg1],1f\n"
+ " stg %[reg1],8(%[psw_pgm])\n"
" tprot 0(%[addr]),0\n"
" ipm %[rc]\n"
" srl %[rc],28\n"
- "1:\n"
- : [pgm_addr] "=&d"(pgm_addr),
- [psw_pgm_addr] "=Q"(S390_lowcore.program_new_psw.addr),
- [rc] "+&d"(rc)
- : [addr] "a"(addr)
+ "1: mvc 0(16,%[psw_pgm]),0(%[psw_old])\n"
+ : [reg1] "=&d" (reg1),
+ [reg2] "=&a" (reg2),
+ [rc] "+&d" (rc),
+ "=Q" (S390_lowcore.program_new_psw.addr),
+ "=Q" (old)
+ : [psw_old] "a" (&old),
+ [psw_pgm] "a" (&S390_lowcore.program_new_psw),
+ [addr] "a" (addr)
: "cc", "memory");
- S390_lowcore.program_new_psw = old;
return rc;
}

--
2.30.2