linux-kernel - Re: [PATCH 69/82] perf tools: Refactor intentional wrap-around test

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Message-ID: <dc3a7101-964b-46c5-a78b-374b68cd54fb@intel.com>
Date: Tue, 23 Jan 2024 08:21:41 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Ian Rogers <irogers@...gle.com>, John Garry <john.garry@...wei.com>,
 Fangrui Song <maskray@...gle.com>, linux-perf-users@...r.kernel.org,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 69/82] perf tools: Refactor intentional wrap-around test

On 23/01/24 02:27, Kees Cook wrote:
> In an effort to separate intentional arithmetic wrap-around from
> unexpected wrap-around, we need to refactor places that depend on this
> kind of math. One of the most common code patterns of this is:
> 
> 	VAR + value < VAR
> 
> Notably, this is considered "undefined behavior" for signed and pointer
> types, which the kernel works around by using the -fno-strict-overflow
> option in the build[1] (which used to just be -fwrapv). Regardless, we
> want to get the kernel source to the position where we can meaningfully
> instrument arithmetic wrap-around conditions and catch them when they
> are unexpected, regardless of whether they are signed[2], unsigned[3],
> or pointer[4] types.
> 
> Refactor open-coded wrap-around addition test to use add_would_overflow().
> This paves the way to enabling the wrap-around sanitizers in the future.
> 
> Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
> Link: https://github.com/KSPP/linux/issues/26 [2]
> Link: https://github.com/KSPP/linux/issues/27 [3]
> Link: https://github.com/KSPP/linux/issues/344 [4]
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: John Garry <john.garry@...wei.com>
> Cc: Fangrui Song <maskray@...gle.com>
> Cc: linux-perf-users@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  tools/perf/util/dso.c                    | 2 +-
>  tools/perf/util/unwind-libdw.c           | 2 +-
>  tools/perf/util/unwind-libunwind-local.c | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 22fd5fa806ed..470a86f1cdfd 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -1122,7 +1122,7 @@ static ssize_t data_read_write_offset(struct dso *dso, struct machine *machine,
>  	if (offset > dso->data.file_size)
>  		return -1;
>  
> -	if (offset + size < offset)
> +	if (add_would_overflow(offset, size))

perf tools has separate includes to the kernel, so does not
seem to include add_would_overflow() in any of its include
files at this point.  Need to update
tools/include/linux/overflow.h first.