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

Commit Message

Christophe Leroy March 1, 2024, 7:57 a.m. UTC

set_memory_ro() can fail, leaving memory unprotected.

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

Link: https://github.com/KSPP/linux/issues/7
Signed-off-by: Christophe Leroy <[e-mail]>
Cc: [e-mail] <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
---
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 https://lore.kernel.org/bpf/wvd5gzde5ejc2rzsbrtwqyof56uw5ea3rxntfrxtkdabzcuwt6@w7iczzhmay2i/T/#m2e61446f42d5dc3d78f2e0e8b7a783f15cfb109d
---
 include/linux/filter.h | 5 +++--
 kernel/bpf/core.c      | 4 +++-
 kernel/bpf/verifier.c  | 4 +++-
 3 files changed, 9 insertions(+), 4 deletions(-)

Comments

Daniel Borkmann March 7, 2024, 5:30 p.m. UTC | #1

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.
> 
> Link: https://github.com/KSPP/linux/issues/7
> Signed-off-by: Christophe Leroy <[e-mail]>
> Cc: [e-mail] <[e-mail]>
> Reviewed-by: Kees Cook <[e-mail]>
> ---
> 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 https://lore.kernel.org/bpf/wvd5gzde5ejc2rzsbrtwqyof56uw5ea3rxntfrxtkdabzcuwt6@w7iczzhmay2i/T/#m2e61446f42d5dc3d78f2e0e8b7a783f15cfb109d
> ---
>   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)
>   {
>   #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>   	if (!fp->jited) {
>   		set_vm_flush_reset_perms(fp);
> -		set_memory_ro((unsigned long)fp, fp->pages);
> +		return set_memory_ro((unsigned long)fp, fp->pages);
>   	}
>   #endif
> +	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)
>   	}
>   
>   finalize:
> -	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.

>   		bpf_prog_kallsyms_add(func[i]);
>   	}
>   
>

Patch

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)
 {
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
 	if (!fp->jited) {
 		set_vm_flush_reset_perms(fp);
-		set_memory_ro((unsigned long)fp, fp->pages);
+		return set_memory_ro((unsigned long)fp, fp->pages);
 	}
 #endif
+	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)
 	}
 
 finalize:
-	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;
 		bpf_prog_kallsyms_add(func[i]);
 	}