bpf: Move constants blinding out of arch-specific JITs

During the JIT stage, constants blinding rewrites instructions but only
rewrites the private instruction copy of the JITed subprog, leaving the
global env->prog->insnsi and env->insn_aux_data untouched. This causes a
mismatch between subprog instructions and the global state, making it
difficult to use the global data in the JIT.

To avoid this mismatch, and given that all arch-specific JITs already
support constants blinding, move it to the generic verifier code, and
switch to rewrite the global env->prog->insnsi with the global states
adjusted, as other rewrites in the verifier do.

This removes the constants blinding calls in each JIT, which are largely
duplicated code across architectures.

Since constants blinding is only required for JIT, and there are two
JIT entry functions, jit_subprogs() for BPF programs with multiple
subprogs and bpf_prog_select_runtime() for programs with no subprogs,
move the constants blinding invocation into these two functions.

In the verifier path, bpf_patch_insn_data() is used to keep global
verifier auxiliary data in sync with patched instructions. A key
question is whether this global auxiliary data should be restored
on the failure path.

Besides instructions, bpf_patch_insn_data() adjusts:
  - prog->aux->poke_tab
  - env->insn_array_maps
  - env->subprog_info
  - env->insn_aux_data

For prog->aux->poke_tab, it is only used by JIT or only meaningful after
JIT succeeds, so it does not need to be restored on the failure path.

For env->insn_array_maps, when JIT fails, programs using insn arrays
are rejected by bpf_insn_array_ready() due to missing JIT addresses.
Hence, env->insn_array_maps is only meaningful for JIT and does not need
to be restored.

For subprog_info, if jit_subprogs fails and CONFIG_BPF_JIT_ALWAYS_ON
is not enabled, kernel falls back to interpreter. In this case,
env->subprog_info is used to determine subprogram stack depth. So it
must be restored on failure.

For env->insn_aux_data, it is freed by clear_insn_aux_data() at the
end of bpf_check(). Before freeing, clear_insn_aux_data() loops over
env->insn_aux_data to release jump targets recorded in it. The loop
uses env->prog->len as the array length, but this length no longer
matches the actual size of the adjusted env->insn_aux_data array after
constants blinding.

To address it, a simple approach is to keep insn_aux_data as adjusted
after failure, since it will be freed shortly, and record its actual size
for the loop in clear_insn_aux_data(). But since clear_insn_aux_data()
uses the same index to loop over both env->prog->insnsi and env->insn_aux_data,
this approach results in incorrect index for the insnsi array. So an
alternative approach is adopted: clone the original env->insn_aux_data
before blinding and restore it after failure, similar to env->prog.

For classic BPF programs, constants blinding works as before since it
is still invoked from bpf_prog_select_runtime().

Reviewed-by: Anton Protopopov <a.s.protopopov@gmail.com> # v8
Reviewed-by: Hari Bathini <hbathini@linux.ibm.com> # powerpc jit
Reviewed-by: Pu Lehui <pulehui@huawei.com> # riscv jit
Acked-by: Hengqi Chen <hengqi.chen@gmail.com> # loongarch jit
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/r/20260416064341.151802-2-xukuohai@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 14 insertions, 25 deletions

diff --git a/arch/arc/net/bpf_jit_core.c b/arch/arc/net/bpf_jit_core.c
index 1421eeced0f5..973ceae48675 100644
--- a/arch/arc/net/bpf_jit_core.c
+++ b/arch/arc/net/bpf_jit_core.c
@@ -79,7 +79,6 @@ struct arc_jit_data {
  * The JIT pertinent context that is used by different functions.
  *
  * prog:		The current eBPF program being handled.
- * orig_prog:		The original eBPF program before any possible change.
  * jit:			The JIT buffer and its length.
  * bpf_header:		The JITed program header. "jit.buf" points inside it.
  * emit:		If set, opcodes are written to memory; else, a dry-run.
@@ -94,12 +93,10 @@ struct arc_jit_data {
  * need_extra_pass:	A forecast if an "extra_pass" will occur.
  * is_extra_pass:	Indicates if the current pass is an extra pass.
  * user_bpf_prog:	True, if VM opcodes come from a real program.
- * blinded:		True if "constant blinding" step returned a new "prog".
  * success:		Indicates if the whole JIT went OK.
  */
 struct jit_context {
 	struct bpf_prog			*prog;
-	struct bpf_prog			*orig_prog;
 	struct jit_buffer		jit;
 	struct bpf_binary_header	*bpf_header;
 	bool				emit;
@@ -114,7 +111,6 @@ struct jit_context {
 	bool				need_extra_pass;
 	bool				is_extra_pass;
 	bool				user_bpf_prog;
-	bool				blinded;
 	bool				success;
 };
 
@@ -161,13 +157,7 @@ static int jit_ctx_init(struct jit_context *ctx, struct bpf_prog *prog)
 {
 	memset(ctx, 0, sizeof(*ctx));
 
-	ctx->orig_prog = prog;
-
-	/* If constant blinding was requested but failed, scram. */
-	ctx->prog = bpf_jit_blind_constants(prog);
-	if (IS_ERR(ctx->prog))
-		return PTR_ERR(ctx->prog);
-	ctx->blinded = (ctx->prog != ctx->orig_prog);
+	ctx->prog = prog;
 
 	/* If the verifier doesn't zero-extend, then we have to do it. */
 	ctx->do_zext = !ctx->prog->aux->verifier_zext;
@@ -214,14 +204,6 @@ static inline void maybe_free(struct jit_context *ctx, void **mem)
  */
 static void jit_ctx_cleanup(struct jit_context *ctx)
 {
-	if (ctx->blinded) {
-		/* if all went well, release the orig_prog. */
-		if (ctx->success)
-			bpf_jit_prog_release_other(ctx->prog, ctx->orig_prog);
-		else
-			bpf_jit_prog_release_other(ctx->orig_prog, ctx->prog);
-	}
-
 	maybe_free(ctx, (void **)&ctx->bpf2insn);
 	maybe_free(ctx, (void **)&ctx->jit_data);
 
@@ -229,12 +211,19 @@ static void jit_ctx_cleanup(struct jit_context *ctx)
 		ctx->bpf2insn_valid = false;
 
 	/* Freeing "bpf_header" is enough. "jit.buf" is a sub-array of it. */
-	if (!ctx->success && ctx->bpf_header) {
-		bpf_jit_binary_free(ctx->bpf_header);
-		ctx->bpf_header = NULL;
-		ctx->jit.buf    = NULL;
-		ctx->jit.index  = 0;
-		ctx->jit.len    = 0;
+	if (!ctx->success) {
+		if (ctx->bpf_header) {
+			bpf_jit_binary_free(ctx->bpf_header);
+			ctx->bpf_header = NULL;
+			ctx->jit.buf    = NULL;
+			ctx->jit.index  = 0;
+			ctx->jit.len    = 0;
+		}
+		if (ctx->is_extra_pass) {
+			ctx->prog->bpf_func = NULL;
+			ctx->prog->jited = 0;
+			ctx->prog->jited_len = 0;
+		}
 	}
 
 	ctx->emit = false;