linux-kernel - Re: [PATCH v2] x86/insn, tools/x86: Fix some potential undefined behavior.

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Date:   Fri, 16 Oct 2020 10:33:30 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Numfor Mbiziwo-Tiapo <nums@...gle.com>
Subject: Re: [PATCH v2] x86/insn, tools/x86: Fix some potential undefined
 behavior.

On Thu, 15 Oct 2020 09:12:16 -0700
Ian Rogers <irogers@...gle.com> wrote:

> From: Numfor Mbiziwo-Tiapo <nums@...gle.com>
> 
> 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 the tools version of the code and perf test. Part of this
> patch was previously posted here:
> https://lore.kernel.org/lkml/20190724184512.162887-4-nums@google.com/
> 
> v2. removes the validate_next check and merges the 2 changes into one as
> requested by Masami Hiramatsu <mhiramat@...nel.org>

Looks good to me. This may be OK on x86, but now this code will be run
on other arches for cross compilation.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you,

> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
> ---
>  arch/x86/lib/insn.c       | 4 ++--
>  tools/arch/x86/lib/insn.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
> index 404279563891..be88ab250146 100644
> --- a/arch/x86/lib/insn.c
> +++ b/arch/x86/lib/insn.c
> @@ -20,10 +20,10 @@
>  	((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); })
> diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
> index 0151dfc6da61..92358c71a59e 100644
> --- a/tools/arch/x86/lib/insn.c
> +++ b/tools/arch/x86/lib/insn.c
> @@ -20,10 +20,10 @@
>  	((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@...nel.org>