Re: [PATCH 2/2] tools/x86: Fix some potential undefined behavior

Masami Hiramatsu
2020-10-15T08:31:39Z

Hi,

Please merge the change on arch/x86/lib/insn.c and tools/arch/x86/lib/insn.c
to a single patch for bisecting.

Thank you,

On Wed, 14 Oct 2020 23:21:48 -0700
Ian Rogers <irogers@google.com> wrote:

> From: Numfor Mbiziwo-Tiapo <nums@google.com>
>
> If insn_init is given a NULL kaddr and 0 buflen then validate_next will
> perform arithmetic on NULL, add a guard to avoid this.
>
> Don't perform unaligned loads in __get_next and __peek_nbyte_next as
> these are forms of undefined behavior.
>
> These problems were identified using the undefined behavior sanitizer
> (ubsan) with perf test. Part of this patch was previously posted here:
> https://lore.kernel.org/lkml/20190724184512.162887-4-nums@google.com/
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
> ---
> tools/arch/x86/lib/insn.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
> index 0151dfc6da61..e8874a8cac2c 100644
> --- a/tools/arch/x86/lib/insn.c
> +++ b/tools/arch/x86/lib/insn.c
> @@ -17,13 +17,13 @@
>
> /* Verify next sizeof(t) bytes can be on the same instruction */
> #define validate_next(t, insn, n) \
> - ((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
> + ((insn)->end_kaddr != 0 && (insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
>
> #define __get_next(t, insn) \
> - ({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); r; })
> + ({ t r; memcpy(&r, insn->next_byte, sizeof(t)); insn->next_byte += sizeof(t); r; })
>
> #define __peek_nbyte_next(t, insn, n) \
> - ({ t r = *(t*)((insn)->next_byte + n); r; })
> + ({ t r; memcpy(&r, (insn)->next_byte + n, sizeof(t)); r; })
>
> #define get_next(t, insn) \
> ({ if (unlikely(!validate_next(t, insn, 0))) goto err_out; __get_next(t, insn); })
> --
> 2.28.0.1011.ga647a8990f-goog
>

--
Masami Hiramatsu <mhiramat@kernel.org>