From: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com
commit 82123a3d1d5a306fdf50c968a474cc60fe43a80f upstream.
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: stable@vger.kernel.org # v5.8+ Reported-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/0df9a032a05576a2fa8e97d1b769af2ff0eafbd6.162141666... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/kprobes.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- 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; }