Guo Ren <guoren@xxxxxxxxxx> writes:
> On Wed, Feb 1, 2023 at 5:40 PM Björn Töpel <bjorn@xxxxxxxxxx> wrote:
>>
>> guoren@xxxxxxxxxx writes:
>>
>> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>> >
>> > The current kprobe would cause a misaligned load for the probe point.
>> > This patch fixup it with two half-word loads instead.
>> >
>> > Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
>> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
>> > Link: https://lore.kernel.org/linux-riscv/878rhig9zj.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>> > Reported-by: Bjorn Topel <bjorn.topel@xxxxxxxxx>
>> > ---
>> > arch/riscv/kernel/probes/kprobes.c | 4 +++-
>> > 1 file changed, 3 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
>> > index 41c7481afde3..c1160629cef4 100644
>> > --- a/arch/riscv/kernel/probes/kprobes.c
>> > +++ b/arch/riscv/kernel/probes/kprobes.c
>> > @@ -74,7 +74,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>> > return -EILSEQ;
>> >
>> > /* copy instruction */
>> > - p->opcode = *p->addr;
>> > + p->opcode = (kprobe_opcode_t)(*(u16 *)probe_addr);
>> > + if (GET_INSN_LENGTH(p->opcode) == 4)
>> > + p->opcode |= (kprobe_opcode_t)(*(u16 *)(probe_addr + 2))
>> > << 16;
>>
>> Ugh, those casts. :-( What about the memcpy variant you had in the other
>> thread?
> The memcpy version would force load probe_addr + 2. This one would
> save an lh operation. The code text guarantees half-word alignment. No
> misaligned load happened. Second, kprobe wouldn't write the last half
> of 32b instruction.
Ok, something more readable, like:
diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index f21592d20306..3602352ba175 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -50,14 +50,16 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
- unsigned long probe_addr = (unsigned long)p->addr;
+ u16 *insn = (u16 *)p->addr;
- if (probe_addr & 0x1)
+ if ((uintptr_t)insn & 0x1)
return -EILSEQ;
/* copy instruction */
- p->opcode = *p->addr;
-
+ p->opcode = *insn++;
+ if (GET_INSN_LENGTH(p->opcode) == 4)
+ p->opcode |= *insn << 16;
+
/* decode instruction */
switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
case INSN_REJECTED: /* insn not supported */
Björn
