Re: [PATCH v2 2/2] x86/cfi,bpf: Fix BPF JIT call

Peter Zijlstra
2023-12-04T12:52:58Z

On Mon, Dec 04, 2023 at 12:11:28PM +0100, Peter Zijlstra wrote:
> On Mon, Dec 04, 2023 at 10:13:34AM +0100, Peter Zijlstra wrote:
>
> > > Just running test_progs it splats right away:
> > >
> > > [ 74.047757] kmemleak: Found object by alias at 0xffffffffa0001d80
> > > [ 74.048272] CPU: 14 PID: 104 Comm: kworker/14:0 Tainted: G W
> > > O 6.7.0-rc3-00702-g41c30fec304d-dirty #5241
> > > [ 74.049118] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > > BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> > > [ 74.050042] Workqueue: events bpf_prog_free_deferred
> > > [ 74.050448] Call Trace:
> > > [ 74.050663] <TASK>
> > > [ 74.050841] dump_stack_lvl+0x55/0x80
> > > [ 74.051141] __find_and_remove_object+0xdb/0x110
> > > [ 74.051521] kmemleak_free+0x41/0x70
> > > [ 74.051828] vfree+0x36/0x130
> >
> > Durr, I'll see if I can get that stuff running locally, and otherwise
> > play with the robot as you suggested. Thanks!
>
> I think it is bpf_jit_binary_pack_hdr(), which is using prog->bpf_func
> as a start address for the image, instead of jit_data->image.
>
> This used to be true, but now it's offset.
>
> Let me see what to do about that...

Not the prettiest of things, but the below seems to make the thing
happy...

---
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 196cc1481dec..f4357c3211bc 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -3024,6 +3024,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
prog->bpf_func = (void *)image + ctx.prog_offset;
prog->jited = 1;
prog->jited_len = proglen - ctx.prog_offset;
+ prog->aux->cfi_offset = ctx.prog_offset;
} else {
prog = orig_prog;
}
@@ -3078,6 +3079,7 @@ void bpf_jit_free(struct bpf_prog *prog)
kvfree(jit_data->addrs);
kfree(jit_data);
}
+ prog->bpf_func = (void *)prog->bpf_func - prog->aux->cfi_offset;
hdr = bpf_jit_binary_pack_hdr(prog);
bpf_jit_binary_pack_free(hdr, NULL);
WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(prog));
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8b725776e70a..e5fa0852a20f 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1483,6 +1483,7 @@ struct bpf_prog_aux {
struct work_struct work;
struct rcu_head rcu;
};
+ u32 cfi_offset;
};

struct bpf_prog {
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5c84a935ba63..763742f4740f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -121,6 +121,9 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag
#endif

INIT_LIST_HEAD_RCU(&fp->aux->ksym.lnode);
+#ifdef CONFIG_FINEIBT
+ INIT_LIST_HEAD_RCU(&fp->aux->ksym_prefix.lnode);
+#endif
mutex_init(&fp->aux->used_maps_mutex);
mutex_init(&fp->aux->dst_mutex);

@@ -709,6 +712,8 @@ void bpf_prog_kallsyms_del(struct bpf_prog *fp)

bpf_ksym_del(&fp->aux->ksym);
#ifdef CONFIG_FINEIBT
+ if (cfi_mode != CFI_FINEIBT)
+ return;
bpf_ksym_del(&fp->aux->ksym_prefix);
#endif
}