powerpc/kprobes: Don't allow breakpoints on suffixes

Do not allow inserting breakpoints on the suffix of a prefix instruction
in kprobes.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-28-jniethe5@gmail.com

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 33d54b0..227510d 100644 (file)
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -106,7 +106,9 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
 int arch_prepare_kprobe(struct kprobe *p)
 {
        int ret = 0;
+       struct kprobe *prev;
        struct ppc_inst insn = ppc_inst_read((struct ppc_inst *)p->addr);
+       struct ppc_inst prefix = ppc_inst_read((struct ppc_inst *)(p->addr - 1));
 
        if ((unsigned long)p->addr & 0x03) {
                printk("Attempt to register kprobe at an unaligned address\n");
@@ -114,6 +116,17 @@ int arch_prepare_kprobe(struct kprobe *p)
        } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
                printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
                ret = -EINVAL;
+       } else if (ppc_inst_prefixed(prefix)) {
+               printk("Cannot register a kprobe on the second word of prefixed instruction\n");
+               ret = -EINVAL;
+       }
+       preempt_disable();
+       prev = get_kprobe(p->addr - 1);
+       preempt_enable_no_resched();
+       if (prev &&
+           ppc_inst_prefixed(ppc_inst_read((struct ppc_inst *)prev->ainsn.insn))) {
+               printk("Cannot register a kprobe on the second word of prefixed instruction\n");
+               ret = -EINVAL;
        }
 
        /* insn must be on a special executable page on ppc64.  This is