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

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

[Kees Cook]

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@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Fangrui Song <maskray@google.com>
Cc: linux-perf-users@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.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))
 		return -1;
 
 	return cached_io(dso, machine, offset, data, size, out);
diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index 6013335a8dae..45a89cbb2c8d 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -198,7 +198,7 @@ static bool memory_read(Dwfl *dwfl __maybe_unused, Dwarf_Addr addr, Dwarf_Word *
 	end = start + stack->size;
 
 	/* Check overflow. */
-	if (addr + sizeof(Dwarf_Word) < addr)
+	if (add_would_overflow(addr, sizeof(Dwarf_Word)))
 		return false;
 
 	if (addr < start || addr + sizeof(Dwarf_Word) > end) {
diff --git a/tools/perf/util/unwind-libunwind-local.c b/tools/perf/util/unwind-libunwind-local.c
index dac536e28360..ac71cc7f53b9 100644
--- a/tools/perf/util/unwind-libunwind-local.c
+++ b/tools/perf/util/unwind-libunwind-local.c
@@ -587,7 +587,7 @@ static int access_mem(unw_addr_space_t __maybe_unused as,
 	end = start + stack->size;
 
 	/* Check overflow. */
-	if (addr + sizeof(unw_word_t) < addr)
+	if (add_would_overflow(addr, sizeof(unw_word_t)))
 		return -EINVAL;
 
 	if (addr < start || addr + sizeof(unw_word_t) >= end) {
-- 
2.34.1

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

[Adrian Hunter]

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@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Ian Rogers <irogers@google.com>
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Cc: John Garry <john.garry@huawei.com>
> Cc: Fangrui Song <maskray@google.com>
> Cc: linux-perf-users@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.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.

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

[Kees Cook]

On Tue, Jan 23, 2024 at 08:21:41AM +0200, Adrian Hunter wrote:
> 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.

Oops, thank you! I will adjust this.

-- 
Kees Cook