[PATCH v4 1/3] riscv: kprobes: fix out-of-bounds read in riscv_probe_decode_insn

[Vladimir Kondratiev]

riscv_probe_decode_insn() can trigger an out-of-bounds page fault
when probing a 16-bit compressed instruction at the end of a page.

arch_prepare_kprobe() safely reads 16-bit parcels into p->opcode, but then
passes p->addr to riscv_probe_decode_insn(), which unconditionally
dereferences *addr as a 32-bit probe_opcode_t

If a 16-bit instruction sits in the last two bytes of a mapped page next
to an unmapped page, the 32-bit read of *addr crosses the page boundary
and faults.

Passing &p->opcode instead of p->addr to riscv_probe_decode_insn()
(as arch_uprobe_analyze_insn() already does) avoid reading past the
instruction.

Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Closes: https://sashiko.dev/#/bug/linux-812af091-20d1-4915-97a6-741f51e07022
Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
Reviewed-by: GUO Ren (XuanTie) <guoren@xxxxxxxxxx>
Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev@xxxxxxxxxxxx>
---
 arch/riscv/kernel/probes/kprobes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 9e2afabf94e8..63ee5066def5 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -85,7 +85,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 		p->opcode |= (kprobe_opcode_t)(*insn) << 16;
 
 	/* decode instruction */
-	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
+	switch (riscv_probe_decode_insn(&p->opcode, &p->ainsn.api)) {
 	case INSN_REJECTED:	/* insn not supported */
 		return -EINVAL;
 

-- 
2.43.0