[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@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: John Garry <john.garry@xxxxxxxxxx>
Cc: Fangrui Song <maskray@xxxxxxxxxx>
Cc: linux-perf-users@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 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