bpf: Add helper macro bpf_for_each_reg_in_vstate

For a lot of use cases in future patches, we will want to modify the
state of registers part of some same 'group' (e.g. same ref_obj_id). It
won't just be limited to releasing reference state, but setting a type
flag dynamically based on certain actions, etc.

Hence, we need a way to easily pass a callback to the function that
iterates over all registers in current bpf_verifier_state in all frames
upto (and including) the curframe.

While in C++ we would be able to easily use a lambda to pass state and
the callback together, sadly we aren't using C++ in the kernel. The next
best thing to avoid defining a function for each case seems like
statement expressions in GNU C. The kernel already uses them heavily,
hence they can passed to the macro in the style of a lambda. The
statement expression will then be substituted in the for loop bodies.

Variables __state and __reg are set to current bpf_func_state and reg
for each invocation of the expression inside the passed in verifier
state.

Then, convert mark_ptr_or_null_regs, clear_all_pkt_pointers,
release_reference, find_good_pkt_pointers, find_equal_scalars to
use bpf_for_each_reg_in_vstate.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220904204145.3089-16-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 8fbc1d05281e..b49a349cc6ae 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -348,6 +348,27 @@ struct bpf_verifier_state {
 	     iter < frame->allocated_stack / BPF_REG_SIZE;		\
 	     iter++, reg = bpf_get_spilled_reg(iter, frame))
 
+/* Invoke __expr over regsiters in __vst, setting __state and __reg */
+#define bpf_for_each_reg_in_vstate(__vst, __state, __reg, __expr)   \
+	({                                                               \
+		struct bpf_verifier_state *___vstate = __vst;            \
+		int ___i, ___j;                                          \
+		for (___i = 0; ___i <= ___vstate->curframe; ___i++) {    \
+			struct bpf_reg_state *___regs;                   \
+			__state = ___vstate->frame[___i];                \
+			___regs = __state->regs;                         \
+			for (___j = 0; ___j < MAX_BPF_REG; ___j++) {     \
+				__reg = &___regs[___j];                  \
+				(void)(__expr);                          \
+			}                                                \
+			bpf_for_each_spilled_reg(___j, __state, __reg) { \
+				if (!__reg)                              \
+					continue;                        \
+				(void)(__expr);                          \
+			}                                                \
+		}                                                        \
+	})
+
 /* linked list of verifier states used to prune search */
 struct bpf_verifier_state_list {
 	struct bpf_verifier_state state;