On Wed, Aug 10, 2022 at 3:44 PM Roberto Sassu [off-list ref] wrote:

quoted

From: Jarkko Sakkinen [mailto:jarkko@kernel.org]
Sent: Tuesday, August 9, 2022 6:55 PM
On Tue, Aug 09, 2022 at 03:45:54PM +0200, Roberto Sassu wrote:

quoted

From: Benjamin Tissoires <redacted>

From: Benjamin Tissoires <redacted>

This allows to declare a kfunc as sleepable and prevents its use in
a non sleepable program.

Nit: "Declare a kfunc as sleepable and prevent its use in a
non-sleepable program."

It's missing the part *how* the patch accomplishes its goals.

I will add:

If an eBPF program is going to call a kfunc declared as sleepable,
eBPF will look at the eBPF program flags. If BPF_F_SLEEPABLE is
not set, execution of that program is denied.

All those changes are looking good to me.

Thanks a lot for keeping pushing on this patch :)

Cheers,
Benjamin

Roberto

quoted

quoted

Signed-off-by: Benjamin Tissoires <redacted>
Co-developed-by: Yosry Ahmed <redacted>
Signed-off-by: Yosry Ahmed <redacted>
Signed-off-by: Hao Luo <redacted>
---
 Documentation/bpf/kfuncs.rst | 6 ++++++
 include/linux/btf.h          | 1 +
 kernel/bpf/btf.c             | 9 +++++++++
 3 files changed, 16 insertions(+)

diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index c0b7dae6dbf5..c8b21de1c772 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst

@@ -146,6 +146,12 @@ that operate (change some property, perform some

operation) on an object that

quoted

 was obtained using an acquire kfunc. Such kfuncs need an unchanged pointer

to

quoted

 ensure the integrity of the operation being performed on the expected object.

+2.4.6 KF_SLEEPABLE flag
+-----------------------
+
+The KF_SLEEPABLE flag is used for kfuncs that may sleep. Such kfuncs can

only

quoted

+be called by sleepable BPF programs (BPF_F_SLEEPABLE).
+
 2.5 Registering the kfuncs
 --------------------------

diff --git a/include/linux/btf.h b/include/linux/btf.h
index cdb376d53238..976cbdd2981f 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h

@@ -49,6 +49,7 @@
  * for this case.
  */
 #define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer

arguments */

quoted

+#define KF_SLEEPABLE   (1 << 5) /* kfunc may sleep */

 struct btf;
 struct btf_member;

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 7e64447659f3..d3e4c86b8fcd 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c

@@ -6175,6 +6175,7 @@ static int btf_check_func_arg_match(struct

bpf_verifier_env *env,

quoted

 {
    enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
    bool rel = false, kptr_get = false, trusted_arg = false;
+   bool sleepable = false;
    struct bpf_verifier_log *log = &env->log;
    u32 i, nargs, ref_id, ref_obj_id = 0;
    bool is_kfunc = btf_is_kernel(btf);

@@ -6212,6 +6213,7 @@ static int btf_check_func_arg_match(struct

bpf_verifier_env *env,

quoted

            rel = kfunc_flags & KF_RELEASE;
            kptr_get = kfunc_flags & KF_KPTR_GET;
            trusted_arg = kfunc_flags & KF_TRUSTED_ARGS;
+           sleepable = kfunc_flags & KF_SLEEPABLE;
    }

    /* check that BTF function arguments match actual types that the

@@ -6419,6 +6421,13 @@ static int btf_check_func_arg_match(struct

bpf_verifier_env *env,

quoted

                    func_name);
            return -EINVAL;
    }
+
+   if (sleepable && !env->prog->aux->sleepable) {
+           bpf_log(log, "kernel function %s is sleepable but the program is

not\n",

quoted

+                   func_name);
+           return -EINVAL;
+   }
+
    /* returns argument register number > 0 in case of reference release

kfunc */

quoted

    return rel ? ref_regno : 0;
 }
--
2.25.1

BR, Jarkko