[PATCH v1 05/15] powerpc/align: Don't use __get_user_instr() on kernel addresses

Christophe Leroy
2021-02-25T17:56:52Z

In the old days, when we didn't have kernel userspace access
protection and had set_fs(), it was wise to use __get_user()
and friends to read kernel memory.

Nowadays, get_user() is granting userspace access and is exclusively
for userspace access.

In alignment exception handler, use probe_kernel_read_inst()
instead of __get_user_instr() for reading instructions in kernel.

This will allow to remove the is_kernel_addr() check in
__get/put_user() in a following patch.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/kernel/align.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
index 83b199026a1e..55e262627b53 100644
--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -305,7 +305,11 @@ int fix_alignment(struct pt_regs *regs)
*/
CHECK_FULL_REGS(regs);

- if (unlikely(__get_user_instr(instr, (void __user *)regs->nip)))
+ if (is_kernel_addr(regs->nip))
+ r = probe_kernel_read_inst(&instr, (void *)regs->nip);
+ else
+ r = __get_user_instr(instr, (void __user *)regs->nip);
+ if (unlikely(r))
return -EFAULT;
if ((regs->msr & MSR_LE) != (MSR_KERNEL & MSR_LE)) {
/* We don't handle PPC little-endian any more... */
--
2.25.0