Commit 95acd881 authored by Tony Ambardar's avatar Tony Ambardar Committed by Daniel Borkmann
Browse files

bpf, x64: Add predicate for bpf2bpf with tailcalls support in JIT 



The BPF core/verifier is hard-coded to permit mixing bpf2bpf and tail
calls for only x86-64. Change the logic to instead rely on a new weak
function 'bool bpf_jit_supports_subprog_tailcalls(void)', which a capable
JIT backend can override.

Update the x86-64 eBPF JIT to reflect this.

Signed-off-by: default avatarTony Ambardar <Tony.Ambardar@gmail.com>
[jakub: drop MIPS bits and tweak patch subject]
Signed-off-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220617105735.733938-2-jakub@cloudflare.com
parent b40b414e

arch/x86/net/bpf_jit_comp.c

+6 −0
Original line number Diff line number Diff line
@@ -2491,3 +2491,9 @@ void *bpf_arch_text_copy(void *dst, void *src, size_t len) 
		return ERR_PTR(-EINVAL);

	return dst;

}



/* Indicate the JIT backend supports mixing bpf2bpf and tailcalls. */

bool bpf_jit_supports_subprog_tailcalls(void)

{

	return true;

}

include/linux/filter.h

+1 −0
Original line number Diff line number Diff line
@@ -914,6 +914,7 @@ u64 __bpf_call_base(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5); 
struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog);

void bpf_jit_compile(struct bpf_prog *prog);

bool bpf_jit_needs_zext(void);

bool bpf_jit_supports_subprog_tailcalls(void);

bool bpf_jit_supports_kfunc_call(void);

bool bpf_helper_changes_pkt_data(void *func);

kernel/bpf/core.c

+6 −0
Original line number Diff line number Diff line
@@ -2729,6 +2729,12 @@ bool __weak bpf_jit_needs_zext(void) 
	return false;

}



/* Return TRUE if the JIT backend supports mixing bpf2bpf and tailcalls. */

bool __weak bpf_jit_supports_subprog_tailcalls(void)

{

	return false;

}



bool __weak bpf_jit_supports_kfunc_call(void)

{

	return false;

kernel/bpf/verifier.c

+2 −1
Original line number Diff line number Diff line
@@ -6154,7 +6154,8 @@ static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id) 


static bool allow_tail_call_in_subprogs(struct bpf_verifier_env *env)

{

	return env->prog->jit_requested && IS_ENABLED(CONFIG_X86_64);

	return env->prog->jit_requested &&

	       bpf_jit_supports_subprog_tailcalls();

}



static int check_map_func_compatibility(struct bpf_verifier_env *env,