[PATCH v4 2/2] riscv: kprobes: add KUnit test for LR/SC sequence rejection

[Xiaofeng Yuan <yuanxiaofeng@eswincomputing.com>]

Add a KUnit test that probes an instruction inside and right after an
LR/SC sequence, and check that the former is rejected while the latter
is accepted.

The probe points are declared as local (.L) labels, which are filtered
out of the kallsyms symbol table, so kallsyms_lookup_size_offset()
always resolves to the enclosing function and the forward scan starts
from the correct function boundary.  A probe address that coincided
with a kallsyms symbol would make the offset 0 and skip the scan
entirely.

Signed-off-by: Xiaofeng Yuan <yuanxiaofeng@eswincomputing.com>
---
v4: New in v4: add a dedicated KUnit test for the LR/SC rejection path.
    The existing test_kprobe_riscv only probes ordinary instructions, so
    the LR/SC rejection path was never exercised and the two
    backward-scan bugs went unnoticed.
---
 .../kernel/tests/kprobes/test-kprobes-asm.S   | 19 +++++++++++++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.c | 19 +++++++++++++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.h |  6 ++++++
 3 files changed, 44 insertions(+)

diff --git a/arch/riscv/kernel/tests/kprobes/test-kprobes-asm.S b/arch/riscv/kernel/tests/kprobes/test-kprobes-asm.S
index f16deee9e0..f2c412aedd 100644
--- a/arch/riscv/kernel/tests/kprobes/test-kprobes-asm.S
+++ b/arch/riscv/kernel/tests/kprobes/test-kprobes-asm.S
@@ -181,6 +181,25 @@ SYM_FUNC_END(test_kprobes_c_bnez)
 
 #endif /* CONFIG_RISCV_ISA_C */
 
+SYM_FUNC_START(test_kprobes_lrsc)
+	li a0, 1
+1:
+	lr.w a1, 0(x0)
+.Llrsc_inside:
+	addi a1, a1, 1
+	sc.w a2, a1, 0(x0)
+	bnez a2, 1b
+.Llrsc_after:
+	li a0, KPROBE_TEST_MAGIC
+	ret
+SYM_FUNC_END(test_kprobes_lrsc)
+
+.section .rodata
+SYM_DATA_START(test_kprobes_lrsc_offsets)
+	RISCV_PTR .Llrsc_inside - test_kprobes_lrsc
+	RISCV_PTR .Llrsc_after - test_kprobes_lrsc
+SYM_DATA_END(test_kprobes_lrsc_offsets)
+
 .section .rodata
 SYM_DATA_START(test_kprobes_addresses)
 	RISCV_PTR test_kprobes_add_addr1
diff --git a/arch/riscv/kernel/tests/kprobes/test-kprobes.c b/arch/riscv/kernel/tests/kprobes/test-kprobes.c
index 027424a3ff..25bd103e20 100644
--- a/arch/riscv/kernel/tests/kprobes/test-kprobes.c
+++ b/arch/riscv/kernel/tests/kprobes/test-kprobes.c
@@ -43,8 +43,27 @@ static void test_kprobe_riscv(struct kunit *test)
 	kfree(kp);
 }
 
+static void test_kprobe_lrsc(struct kunit *test)
+{
+	struct kprobe kp = {};
+
+	kp.pre_handler = kprobe_dummy_handler;
+
+	/* a probe inside an LR/SC sequence must be rejected */
+	kp.addr = (kprobe_opcode_t *)((unsigned long)test_kprobes_lrsc +
+				      test_kprobes_lrsc_offsets[0]);
+	KUNIT_EXPECT_LT(test, register_kprobe(&kp), 0);
+
+	/* a probe right after the sequence must be accepted */
+	kp.addr = (kprobe_opcode_t *)((unsigned long)test_kprobes_lrsc +
+				      test_kprobes_lrsc_offsets[1]);
+	KUNIT_EXPECT_EQ(test, 0, register_kprobe(&kp));
+	unregister_kprobe(&kp);
+}
+
 static struct kunit_case kprobes_testcases[] = {
 	KUNIT_CASE(test_kprobe_riscv),
+	KUNIT_CASE(test_kprobe_lrsc),
 	{}
 };
 
diff --git a/arch/riscv/kernel/tests/kprobes/test-kprobes.h b/arch/riscv/kernel/tests/kprobes/test-kprobes.h
index 537f44aa9d..58be980fdf 100644
--- a/arch/riscv/kernel/tests/kprobes/test-kprobes.h
+++ b/arch/riscv/kernel/tests/kprobes/test-kprobes.h
@@ -19,6 +19,12 @@ extern void *test_kprobes_addresses[];
 /* array of functions that return KPROBE_TEST_MAGIC */
 extern long (*test_kprobes_functions[])(void);
 
+/* function containing an LR/SC sequence, and offsets (from its start) of
+ * the instruction inside and right after the sequence
+ */
+extern void test_kprobes_lrsc(void);
+extern unsigned long test_kprobes_lrsc_offsets[];
+
 #endif /* __ASSEMBLER__ */
 
 #endif /* TEST_KPROBES_H */
-- 
2.43.0


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