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[RFC,bpf-next,v1,8/9] bpf: Introduce BPF assertion macros

Message ID 20230405004239.1375399-9-memxor@gmail.com (mailing list archive)
State RFC
Delegated to: BPF
Headers show
Series Exceptions - 1/2 | expand

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bpf/vmtest-bpf-next-PR success PR summary
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bpf/vmtest-bpf-next-VM_Test-4 pending Logs for build for s390x with gcc
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bpf/vmtest-bpf-next-VM_Test-6 success Logs for build for x86_64 with llvm-16
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 20 this patch: 20
netdev/cc_maintainers warning 11 maintainers not CCed: mykolal@fb.com song@kernel.org shuah@kernel.org sdf@google.com haoluo@google.com yhs@fb.com john.fastabend@gmail.com kpsingh@kernel.org jolsa@kernel.org martin.lau@linux.dev linux-kselftest@vger.kernel.org
netdev/build_clang success Errors and warnings before: 18 this patch: 18
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 20 this patch: 20
netdev/checkpatch fail ERROR: Macros with multiple statements should be enclosed in a do - while loop ERROR: space prohibited before that ',' (ctx:WxW) WARNING: line length of 100 exceeds 80 columns WARNING: sizeof(& should be avoided
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Kumar Kartikeya Dwivedi April 5, 2023, 12:42 a.m. UTC 
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@gmail.com>
---
 tools/testing/selftests/bpf/bpf_experimental.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
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Patch

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