Re: [PATCH bpf-next] arm64,bpf: Support struct arguments in the BPF trampoline
From: Xu Kuohai
Date: Wed May 10 2023 - 03:07:15 EST
On 5/9/2023 12:46 AM, Florent Revest wrote:
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@xxxxxxxxxxxx>
---
arch/arm64/net/bpf_jit_comp.c | 51 ++++++++++----------
tools/testing/selftests/bpf/DENYLIST.aarch64 | 1 -
2 files changed, 26 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index b26da8efa616..22e3c456554f 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -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];
@@ -1799,7 +1799,7 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
* [ ... ]
* SP + args_off [ arg1 ]
*
- * SP + nargs_off [ args count ]
+ * SP + nregs_off [ arg regs count ]
For description consistency, should arg1 ... argN in the previous
lines also be changed to arg reg 1 ... arg reg N?
*
* 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;
diff --git a/tools/testing/selftests/bpf/DENYLIST.aarch64 b/tools/testing/selftests/bpf/DENYLIST.aarch64
index cd42e2825bd2..08adc805878b 100644
--- a/tools/testing/selftests/bpf/DENYLIST.aarch64
+++ b/tools/testing/selftests/bpf/DENYLIST.aarch64
@@ -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)