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 <pet...@infradead.org>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
Cc: Mark Rutland <mark.rutl...@arm.com>
Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
Cc: Jiri Olsa <jo...@kernel.org>
Cc: Namhyung Kim <namhy...@kernel.org>
Cc: Ian Rogers <irog...@google.com>
Cc: Adrian Hunter <adrian.hun...@intel.com>
Cc: John Garry <john.ga...@huawei.com>
Cc: Fangrui Song <mask...@google.com>
Cc: linux-perf-us...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@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
