Re: [PATCH bpf-next RESEND v2 1/2] bpf: Take return from set_memory_ro() into account with bpf_prog_lock_ro()

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On 3/1/24 8:57 AM, Christophe Leroy wrote:
set_memory_ro() can fail, leaving memory unprotected.

Check its return and take it into account as an error.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: linux-hardening@xxxxxxxxxxxxxxx <linux-hardening@xxxxxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Sorry for the resend, I forgot to flag patch 2 as bpf-next

Note: next patch is autonomous, it is sent as a follow-up of this one to minimize risk of conflict on filter.h because the two changes are too close to each other.

v2: No modification (Just added link in patch message), patchwork discarded this series due to failed test of s390 but it seems unrelated, see
  include/linux/filter.h | 5 +++--
  kernel/bpf/core.c      | 4 +++-
  kernel/bpf/verifier.c  | 4 +++-
  3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 36cc29a2934c..7dd59bccaeec 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -884,14 +884,15 @@ bpf_ctx_narrow_access_offset(u32 off, u32 size, u32 size_default)
#define bpf_classic_proglen(fprog) (fprog->len * sizeof(fprog->filter[0])) -static inline void bpf_prog_lock_ro(struct bpf_prog *fp)
+static inline int __must_check bpf_prog_lock_ro(struct bpf_prog *fp)
  	if (!fp->jited) {
-		set_memory_ro((unsigned long)fp, fp->pages);
+		return set_memory_ro((unsigned long)fp, fp->pages);
+	return 0;
static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 71c459a51d9e..c49619ef55d0 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2392,7 +2392,9 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
-	bpf_prog_lock_ro(fp);
+	*err = bpf_prog_lock_ro(fp);
+	if (*err)
+		return fp;
/* The tail call compatibility check can only be done at
  	 * this late stage as we need to determine, if we deal
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1c34b91b9583..6ec134f76a11 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19096,7 +19096,9 @@ static int jit_subprogs(struct bpf_verifier_env *env)
  	 * bpf_prog_load will add the kallsyms for the main program.
  	for (i = 1; i < env->subprog_cnt; i++) {
-		bpf_prog_lock_ro(func[i]);
+		err = bpf_prog_lock_ro(func[i]);
+		if (err)
+			goto out_free;

How does the error path take out the subprogs from kallsyms in your case? Suppose some of
the loop iterations succeed before we hit an error. I believe the subprogs still exist in
kallsyms here.


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