Implement macros that allow for asserting conditions for with a given
register and constant value to prove a condition to the verifier, and
safely abort the program in case the condition is not true. The verifier
can still perform dead code elimination of the bpf_throw call if it can
actually prove the condition based on the seen data flow during path
exploration, and the function may not be marked as throwing.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
tools/testing/selftests/bpf/bpf_experimental.h | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index a9c75270e49b..aae358a8db4b 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -109,4 +109,21 @@ extern void bpf_throw(void) __attribute__((noreturn)) __ksym;
*/
extern void bpf_set_exception_callback(int (*)(void)) __ksym;
+#define __bpf_assert_op(LHS, op, RHS) \
+ _Static_assert(sizeof(&(LHS)), "1st argument must be an lvalue expression"); \
+ _Static_assert(__builtin_constant_p((RHS)), "2nd argument must be a constant expression"); \
+ asm volatile ("if %[lhs] " op " %[rhs] goto +1; call bpf_throw" \
+ : : [lhs] "r"(LHS) , [rhs] "i"(RHS) :)
+
+#define bpf_assert_eq(LHS, RHS) __bpf_assert_op(LHS, "==", RHS)
+#define bpf_assert_ne(LHS, RHS) __bpf_assert_op(LHS, "!=", RHS)
+#define bpf_assert_lt(LHS, RHS) __bpf_assert_op(LHS, "<", RHS)
+#define bpf_assert_gt(LHS, RHS) __bpf_assert_op(LHS, ">", RHS)
+#define bpf_assert_le(LHS, RHS) __bpf_assert_op(LHS, "<=", RHS)
+#define bpf_assert_ge(LHS, RHS) __bpf_assert_op(LHS, ">=", RHS)
+#define bpf_assert_slt(LHS, RHS) __bpf_assert_op(LHS, "s<", RHS)
+#define bpf_assert_sgt(LHS, RHS) __bpf_assert_op(LHS, "s>", RHS)
+#define bpf_assert_sle(LHS, RHS) __bpf_assert_op(LHS, "s<=", RHS)
+#define bpf_assert_sge(LHS, RHS) __bpf_assert_op(LHS, "s>=", RHS)
+
#endif
--
2.40.0
