path: root/arch/powerpc
diff options
authorNaveen N. Rao <>2021-05-19 16:17:17 +0530
committerMichael Ellerman <>2021-05-28 21:52:42 +1000
commit82123a3d1d5a306fdf50c968a474cc60fe43a80f (patch)
tree0bc27b73514fbcbcff456603cd3148d3474ba097 /arch/powerpc
parentd72500f992849d31ebae8f821a023660ddd0dcc2 (diff)
powerpc/kprobes: Fix validation of prefixed instructions across page boundary
When checking if the probed instruction is the suffix of a prefixed instruction, we access the instruction at the previous word. If the probed instruction is the very first word of a module, we can end up trying to access an invalid page. Fix this by skipping the check for all instructions at the beginning of a page. Prefixed instructions cannot cross a 64-byte boundary and as such, we don't expect to encounter a suffix as the very first word in a page for kernel text. Even if there are prefixed instructions crossing a page boundary (from a module, for instance), the instruction will be illegal, so preventing probing on the suffix of such prefix instructions isn't worthwhile. Fixes: b4657f7650ba ("powerpc/kprobes: Don't allow breakpoints on suffixes") Cc: # v5.8+ Reported-by: Christophe Leroy <> Signed-off-by: Naveen N. Rao <> Signed-off-by: Michael Ellerman <> Link:
Diffstat (limited to 'arch/powerpc')
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 01ab2163659e..e8c2a6373157 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -108,7 +108,6 @@ 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");
@@ -116,7 +115,8 @@ 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)) {
+ } else if ((unsigned long)p->addr & ~PAGE_MASK &&
+ ppc_inst_prefixed(ppc_inst_read((struct ppc_inst *)(p->addr - 1)))) {
printk("Cannot register a kprobe on the second word of prefixed instruction\n");
ret = -EINVAL;