Commit 535a57a7 authored by Xu Kuohai's avatar Xu Kuohai Committed by Daniel Borkmann
Browse files

bpf: Remove is_valid_bpf_tramp_flags() 



Before generating bpf trampoline, x86 calls is_valid_bpf_tramp_flags()
to check the input flags. This check is architecture independent.
So, to be consistent with x86, arm64 should also do this check
before generating bpf trampoline.

However, the BPF_TRAMP_F_XXX flags are not used by user code and the
flags argument is almost constant at compile time, so this run time
check is a bit redundant.

Remove is_valid_bpf_tramp_flags() and add some comments to the usage of
BPF_TRAMP_F_XXX flags, as suggested by Alexei.

Signed-off-by: default avatarXu Kuohai <xukuohai@huawei.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20220711150823.2128542-2-xukuohai@huawei.com
parent 9974d37e

arch/x86/net/bpf_jit_comp.c

+0 −20
Original line number Diff line number Diff line
@@ -1936,23 +1936,6 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog, 
	return 0;

}



static bool is_valid_bpf_tramp_flags(unsigned int flags)

{

	if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&

	    (flags & BPF_TRAMP_F_SKIP_FRAME))

		return false;



	/*

	 * BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,

	 * and it must be used alone.

	 */

	if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&

	    (flags & ~BPF_TRAMP_F_RET_FENTRY_RET))

		return false;



	return true;

}



/* Example:

 * __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);

 * its 'struct btf_func_model' will be nr_args=2
@@ -2031,9 +2014,6 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i 
	if (nr_args > 6)

		return -ENOTSUPP;



	if (!is_valid_bpf_tramp_flags(flags))

		return -EINVAL;



	/* Generated trampoline stack layout:

	 *

	 * RBP + 8         [ return address  ]

kernel/bpf/bpf_struct_ops.c

+3 −0
Original line number Diff line number Diff line
@@ -341,6 +341,9 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks, 


	tlinks[BPF_TRAMP_FENTRY].links[0] = link;

	tlinks[BPF_TRAMP_FENTRY].nr_links = 1;

	/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,

	 * and it must be used alone.

	 */

	flags = model->ret_size > 0 ? BPF_TRAMP_F_RET_FENTRY_RET : 0;

	return arch_prepare_bpf_trampoline(NULL, image, image_end,

					   model, flags, tlinks, NULL);

kernel/bpf/trampoline.c

+3 −0
Original line number Diff line number Diff line
@@ -360,6 +360,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr) 


	if (tlinks[BPF_TRAMP_FEXIT].nr_links ||

	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)

		/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME

		 * should not be set together.

		 */

		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;



	if (ip_arg)