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bpf, arm64: Support struct arguments in the BPF trampoline

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This extends the BPF trampoline JIT to support attachment to functions
that take small structures (up to 128bit) as argument. This is trivially
achieved by saving/restoring a number of "argument registers" rather
than a number of arguments.

The AAPCS64 section 6.8.2 describes the parameter passing ABI.
"Composite types" (like C structs) below 16 bytes (as enforced by the
BPF verifier) are provided as part of the 8 argument registers as
explained in the section C.12.

Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/bpf/20230511140507.514888-1-revest@chromium.org
This commit is contained in:
Florent Revest 2023-05-11 16:05:07 +02:00 committed by Daniel Borkmann
parent 04cb8453a9
commit 90564f1e3d
2 changed files with 28 additions and 28 deletions
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55
arch/arm64/net/bpf_jit_comp.c
View File

@ -1731,21 +1731,21 @@ static void invoke_bpf_mod_ret(struct jit_ctx *ctx, struct bpf_tramp_links *tl,
}
}
static void save_args(struct jit_ctx *ctx, int args_off, int nargs)
static void save_args(struct jit_ctx *ctx, int args_off, int nregs)
{
int i;
for (i = 0; i < nargs; i++) {
for (i = 0; i < nregs; i++) {
emit(A64_STR64I(i, A64_SP, args_off), ctx);
args_off += 8;
}
}
static void restore_args(struct jit_ctx *ctx, int args_off, int nargs)
static void restore_args(struct jit_ctx *ctx, int args_off, int nregs)
{
int i;
for (i = 0; i < nargs; i++) {
for (i = 0; i < nregs; i++) {
emit(A64_LDR64I(i, A64_SP, args_off), ctx);
args_off += 8;
}
@ -1764,7 +1764,7 @@ static void restore_args(struct jit_ctx *ctx, int args_off, int nargs)
*/
static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
struct bpf_tramp_links *tlinks, void *orig_call,
int nargs, u32 flags)
int nregs, u32 flags)
{
int i;
int stack_size;
@ -1772,7 +1772,7 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
int regs_off;
int retval_off;
int args_off;
int nargs_off;
int nregs_off;
int ip_off;
int run_ctx_off;
struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
@ -1795,11 +1795,11 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
* SP + retval_off [ return value ] BPF_TRAMP_F_CALL_ORIG or
* BPF_TRAMP_F_RET_FENTRY_RET
*
* [ argN ]
* [ arg reg N ]
* [ ... ]
* SP + args_off [ arg1 ]
* SP + args_off [ arg reg 1 ]
*
* SP + nargs_off [ args count ]
* SP + nregs_off [ arg regs count ]
*
* SP + ip_off [ traced function ] BPF_TRAMP_F_IP_ARG flag
*
@ -1816,13 +1816,13 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
if (flags & BPF_TRAMP_F_IP_ARG)
stack_size += 8;
nargs_off = stack_size;
nregs_off = stack_size;
/* room for args count */
stack_size += 8;
args_off = stack_size;
/* room for args */
stack_size += nargs * 8;
stack_size += nregs * 8;
/* room for return value */
retval_off = stack_size;
@ -1865,12 +1865,12 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
emit(A64_STR64I(A64_R(10), A64_SP, ip_off), ctx);
}
/* save args count*/
emit(A64_MOVZ(1, A64_R(10), nargs, 0), ctx);
emit(A64_STR64I(A64_R(10), A64_SP, nargs_off), ctx);
/* save arg regs count*/
emit(A64_MOVZ(1, A64_R(10), nregs, 0), ctx);
emit(A64_STR64I(A64_R(10), A64_SP, nregs_off), ctx);
/* save args */
save_args(ctx, args_off, nargs);
/* save arg regs */
save_args(ctx, args_off, nregs);
/* save callee saved registers */
emit(A64_STR64I(A64_R(19), A64_SP, regs_off), ctx);
@ -1897,7 +1897,7 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
}
if (flags & BPF_TRAMP_F_CALL_ORIG) {
restore_args(ctx, args_off, nargs);
restore_args(ctx, args_off, nregs);
/* call original func */
emit(A64_LDR64I(A64_R(10), A64_SP, retaddr_off), ctx);
emit(A64_ADR(A64_LR, AARCH64_INSN_SIZE * 2), ctx);
@ -1926,7 +1926,7 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
}
if (flags & BPF_TRAMP_F_RESTORE_REGS)
restore_args(ctx, args_off, nargs);
restore_args(ctx, args_off, nregs);
/* restore callee saved register x19 and x20 */
emit(A64_LDR64I(A64_R(19), A64_SP, regs_off), ctx);
@ -1967,24 +1967,25 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
void *orig_call)
{
int i, ret;
int nargs = m->nr_args;
int nregs = m->nr_args;
int max_insns = ((long)image_end - (long)image) / AARCH64_INSN_SIZE;
struct jit_ctx ctx = {
.image = NULL,
.idx = 0,
};
/* the first 8 arguments are passed by registers */
if (nargs > 8)
return -ENOTSUPP;
/* don't support struct argument */
/* extra registers needed for struct argument */
for (i = 0; i < MAX_BPF_FUNC_ARGS; i++) {
/* The arg_size is at most 16 bytes, enforced by the verifier. */
if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
return -ENOTSUPP;
nregs += (m->arg_size[i] + 7) / 8 - 1;
}
ret = prepare_trampoline(&ctx, im, tlinks, orig_call, nargs, flags);
/* the first 8 registers are used for arguments */
if (nregs > 8)
return -ENOTSUPP;
ret = prepare_trampoline(&ctx, im, tlinks, orig_call, nregs, flags);
if (ret < 0)
return ret;
@ -1995,7 +1996,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
ctx.idx = 0;
jit_fill_hole(image, (unsigned int)(image_end - image));
ret = prepare_trampoline(&ctx, im, tlinks, orig_call, nargs, flags);
ret = prepare_trampoline(&ctx, im, tlinks, orig_call, nregs, flags);
if (ret > 0 && validate_code(&ctx) < 0)
ret = -EINVAL;

1
tools/testing/selftests/bpf/DENYLIST.aarch64
View File

@ -10,4 +10,3 @@ kprobe_multi_test/link_api_addrs # link_fd unexpected link_fd: a
kprobe_multi_test/link_api_syms # link_fd unexpected link_fd: actual -95 < expected 0
kprobe_multi_test/skel_api # libbpf: failed to load BPF skeleton 'kprobe_multi': -3
module_attach # prog 'kprobe_multi': failed to auto-attach: -95
tracing_struct # tracing_struct__attach unexpected error: -524 (errno 524)