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Thu, 28 May 2026 05:46:50 -0700 (PDT) From: Jakub Sitnicki To: Jiri Olsa Cc: Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Masami Hiramatsu , Andrii Nakryiko , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCHv4 12/13] selftests/bpf: Add tests for uprobe nop10 red zone clobbering In-Reply-To: <20260526205840.173790-13-jolsa@kernel.org> (Jiri Olsa's message of "Tue, 26 May 2026 22:58:39 +0200") References: <20260526205840.173790-1-jolsa@kernel.org> <20260526205840.173790-13-jolsa@kernel.org> Date: Thu, 28 May 2026 14:46:48 +0200 Message-ID: <87pl2f66rr.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Tue, May 26, 2026 at 10:58 PM +02, Jiri Olsa wrote: > From: Andrii Nakryiko > > The uprobe nop5 optimization used to replace a 5-byte NOP with a 5-byte > CALL to a trampoline. The CALL pushes a return address onto the stack at > [rsp-8], clobbering whatever was stored there. > > On x86-64, the red zone is the 128 bytes below rsp that user code may use > for temporary storage without adjusting rsp. Compilers can place USDT > argument operands there, generating specs like "8@-8(%rbp)" when rbp == > rsp. With the CALL-based optimization, the return address overwrites that > argument before the BPF-side USDT argument fetch runs. > > Add two tests for this case. The uprobe_syscall subtest stores known values > at -8(%rsp), -16(%rsp), and -24(%rsp), executes an optimized nop10 uprobe, > and verifies the red-zone data is still intact. The USDT subtest triggers a > probe in a function where the compiler places three USDT operands in the > red zone and verifies that all 10 optimized invocations deliver the expected > argument values to BPF. > > On an unfixed kernel, the first hit goes through the INT3 path and later > hits use the optimized CALL path, so the red-zone checks fail after > optimization. > > Signed-off-by: Andrii Nakryiko > [ updates to use nop10 ] > Signed-off-by: Jiri Olsa > --- > .../selftests/bpf/prog_tests/uprobe_syscall.c | 75 +++++++++++++++++++ > tools/testing/selftests/bpf/prog_tests/usdt.c | 49 ++++++++++++ > tools/testing/selftests/bpf/progs/test_usdt.c | 25 +++++++ > tools/testing/selftests/bpf/usdt_2.c | 13 ++++ > 4 files changed, 162 insertions(+) > > diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c > index 969f4deba9fd..efff0c515184 100644 > --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c > +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c [...] > @@ -855,6 +897,37 @@ static void test_uprobe_race(void) > #define __NR_uprobe 336 > #endif > > +static void test_uprobe_red_zone(void) > +{ > + struct uprobe_syscall_executed *skel; > + struct bpf_link *link; > + void *nop10_addr; > + size_t offset; > + int i; > + > + nop10_addr = find_nop10(uprobe_red_zone_test); > + if (!ASSERT_NEQ(nop10_addr, NULL, "find_nop10")) Nit: ASSERT_OK_PTR would have worked as well. Dealer's choice. > + return; > + > + skel = uprobe_syscall_executed__open_and_load(); > + if (!ASSERT_OK_PTR(skel, "open_and_load")) > + return; > + > + offset = get_uprobe_offset(nop10_addr); > + link = bpf_program__attach_uprobe_opts(skel->progs.test_uprobe, > + 0, "/proc/self/exe", offset, NULL); > + if (!ASSERT_OK_PTR(link, "attach_uprobe")) > + goto cleanup; > + > + for (i = 0; i < 10; i++) > + ASSERT_EQ(uprobe_red_zone_test(), 0, "red_zone_intact"); > + > + bpf_link__destroy(link); > + > +cleanup: > + uprobe_syscall_executed__destroy(skel); > +} > + > static void test_uprobe_error(void) > { > long err = syscall(__NR_uprobe); [...] Reviewed-by: Jakub Sitnicki