[PATCH bpf-next v3 1/2] bpf: Add arm64 JIT support for PROBE_MEM32 pseudo instructions.
From: Puranjay Mohan
Date: Sat Mar 23 2024 - 06:31:36 EST
Add support for [LDX | STX | ST], PROBE_MEM32, [B | H | W | DW]
instructions. They are similar to PROBE_MEM instructions with the
following differences:
- PROBE_MEM32 supports store.
- PROBE_MEM32 relies on the verifier to clear upper 32-bit of the
src/dst register
- PROBE_MEM32 adds 64-bit kern_vm_start address (which is stored in R28
in the prologue). Due to bpf_arena constructions such R28 + reg +
off16 access is guaranteed to be within arena virtual range, so no
address check at run-time.
- PROBE_MEM32 allows STX and ST. If they fault the store is a nop. When
LDX faults the destination register is zeroed.
To support these on arm64, we do tmp2 = R28 + src/dst reg and then use
tmp2 as the new src/dst register. This allows us to reuse most of the
code for normal [LDX | STX | ST].
Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
---
arch/arm64/net/bpf_jit_comp.c | 70 ++++++++++++++++++++++++++++++-----
1 file changed, 60 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index bc16eb694657..b9b5febe64f0 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -29,6 +29,7 @@
#define TCALL_CNT (MAX_BPF_JIT_REG + 2)
#define TMP_REG_3 (MAX_BPF_JIT_REG + 3)
#define FP_BOTTOM (MAX_BPF_JIT_REG + 4)
+#define PROBE_MEM32_BASE (MAX_BPF_JIT_REG + 5)
#define check_imm(bits, imm) do { \
if ((((imm) > 0) && ((imm) >> (bits))) || \
@@ -67,6 +68,8 @@ static const int bpf2a64[] = {
/* temporary register for blinding constants */
[BPF_REG_AX] = A64_R(9),
[FP_BOTTOM] = A64_R(27),
+ /* callee saved register for kern_vm_start address */
+ [PROBE_MEM32_BASE] = A64_R(28),
};
struct jit_ctx {
@@ -295,7 +298,7 @@ static bool is_lsi_offset(int offset, int scale)
#define PROLOGUE_OFFSET (BTI_INSNS + 2 + PAC_INSNS + 8)
static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf,
- bool is_exception_cb)
+ bool is_exception_cb, u64 arena_vm_start)
{
const struct bpf_prog *prog = ctx->prog;
const bool is_main_prog = !bpf_is_subprog(prog);
@@ -306,6 +309,7 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf,
const u8 fp = bpf2a64[BPF_REG_FP];
const u8 tcc = bpf2a64[TCALL_CNT];
const u8 fpb = bpf2a64[FP_BOTTOM];
+ const u8 pb = bpf2a64[PROBE_MEM32_BASE];
const int idx0 = ctx->idx;
int cur_offset;
@@ -411,6 +415,10 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf,
/* Set up function call stack */
emit(A64_SUB_I(1, A64_SP, A64_SP, ctx->stack_size), ctx);
+
+ if (arena_vm_start)
+ emit_a64_mov_i64(pb, arena_vm_start, ctx);
+
return 0;
}
@@ -738,6 +746,7 @@ static void build_epilogue(struct jit_ctx *ctx, bool is_exception_cb)
#define BPF_FIXUP_OFFSET_MASK GENMASK(26, 0)
#define BPF_FIXUP_REG_MASK GENMASK(31, 27)
+#define DONT_CLEAR 5 /* Unused ARM64 register from BPF's POV */
bool ex_handler_bpf(const struct exception_table_entry *ex,
struct pt_regs *regs)
@@ -745,7 +754,8 @@ bool ex_handler_bpf(const struct exception_table_entry *ex,
off_t offset = FIELD_GET(BPF_FIXUP_OFFSET_MASK, ex->fixup);
int dst_reg = FIELD_GET(BPF_FIXUP_REG_MASK, ex->fixup);
- regs->regs[dst_reg] = 0;
+ if (dst_reg != DONT_CLEAR)
+ regs->regs[dst_reg] = 0;
regs->pc = (unsigned long)&ex->fixup - offset;
return true;
}
@@ -765,7 +775,8 @@ static int add_exception_handler(const struct bpf_insn *insn,
return 0;
if (BPF_MODE(insn->code) != BPF_PROBE_MEM &&
- BPF_MODE(insn->code) != BPF_PROBE_MEMSX)
+ BPF_MODE(insn->code) != BPF_PROBE_MEMSX &&
+ BPF_MODE(insn->code) != BPF_PROBE_MEM32)
return 0;
if (!ctx->prog->aux->extable ||
@@ -810,6 +821,9 @@ static int add_exception_handler(const struct bpf_insn *insn,
ex->insn = ins_offset;
+ if (BPF_CLASS(insn->code) != BPF_LDX)
+ dst_reg = DONT_CLEAR;
+
ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, fixup_offset) |
FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg);
@@ -829,12 +843,13 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
bool extra_pass)
{
const u8 code = insn->code;
- const u8 dst = bpf2a64[insn->dst_reg];
- const u8 src = bpf2a64[insn->src_reg];
+ u8 dst = bpf2a64[insn->dst_reg];
+ u8 src = bpf2a64[insn->src_reg];
const u8 tmp = bpf2a64[TMP_REG_1];
const u8 tmp2 = bpf2a64[TMP_REG_2];
const u8 fp = bpf2a64[BPF_REG_FP];
const u8 fpb = bpf2a64[FP_BOTTOM];
+ const u8 pb = bpf2a64[PROBE_MEM32_BASE];
const s16 off = insn->off;
const s32 imm = insn->imm;
const int i = insn - ctx->prog->insnsi;
@@ -1237,7 +1252,15 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
case BPF_LDX | BPF_PROBE_MEMSX | BPF_B:
case BPF_LDX | BPF_PROBE_MEMSX | BPF_H:
case BPF_LDX | BPF_PROBE_MEMSX | BPF_W:
- if (ctx->fpb_offset > 0 && src == fp) {
+ case BPF_LDX | BPF_PROBE_MEM32 | BPF_B:
+ case BPF_LDX | BPF_PROBE_MEM32 | BPF_H:
+ case BPF_LDX | BPF_PROBE_MEM32 | BPF_W:
+ case BPF_LDX | BPF_PROBE_MEM32 | BPF_DW:
+ if (BPF_MODE(insn->code) == BPF_PROBE_MEM32) {
+ emit(A64_ADD(1, tmp2, src, pb), ctx);
+ src = tmp2;
+ }
+ if (ctx->fpb_offset > 0 && src == fp && BPF_MODE(insn->code) != BPF_PROBE_MEM32) {
src_adj = fpb;
off_adj = off + ctx->fpb_offset;
} else {
@@ -1322,7 +1345,15 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
case BPF_ST | BPF_MEM | BPF_H:
case BPF_ST | BPF_MEM | BPF_B:
case BPF_ST | BPF_MEM | BPF_DW:
- if (ctx->fpb_offset > 0 && dst == fp) {
+ case BPF_ST | BPF_PROBE_MEM32 | BPF_B:
+ case BPF_ST | BPF_PROBE_MEM32 | BPF_H:
+ case BPF_ST | BPF_PROBE_MEM32 | BPF_W:
+ case BPF_ST | BPF_PROBE_MEM32 | BPF_DW:
+ if (BPF_MODE(insn->code) == BPF_PROBE_MEM32) {
+ emit(A64_ADD(1, tmp2, dst, pb), ctx);
+ dst = tmp2;
+ }
+ if (ctx->fpb_offset > 0 && dst == fp && BPF_MODE(insn->code) != BPF_PROBE_MEM32) {
dst_adj = fpb;
off_adj = off + ctx->fpb_offset;
} else {
@@ -1365,6 +1396,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
}
break;
}
+
+ ret = add_exception_handler(insn, ctx, dst);
+ if (ret)
+ return ret;
break;
/* STX: *(size *)(dst + off) = src */
@@ -1372,7 +1407,15 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
case BPF_STX | BPF_MEM | BPF_H:
case BPF_STX | BPF_MEM | BPF_B:
case BPF_STX | BPF_MEM | BPF_DW:
- if (ctx->fpb_offset > 0 && dst == fp) {
+ case BPF_STX | BPF_PROBE_MEM32 | BPF_B:
+ case BPF_STX | BPF_PROBE_MEM32 | BPF_H:
+ case BPF_STX | BPF_PROBE_MEM32 | BPF_W:
+ case BPF_STX | BPF_PROBE_MEM32 | BPF_DW:
+ if (BPF_MODE(insn->code) == BPF_PROBE_MEM32) {
+ emit(A64_ADD(1, tmp2, dst, pb), ctx);
+ dst = tmp2;
+ }
+ if (ctx->fpb_offset > 0 && dst == fp && BPF_MODE(insn->code) != BPF_PROBE_MEM32) {
dst_adj = fpb;
off_adj = off + ctx->fpb_offset;
} else {
@@ -1413,6 +1456,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
}
break;
}
+
+ ret = add_exception_handler(insn, ctx, dst);
+ if (ret)
+ return ret;
break;
case BPF_STX | BPF_ATOMIC | BPF_W:
@@ -1594,6 +1641,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
bool tmp_blinded = false;
bool extra_pass = false;
struct jit_ctx ctx;
+ u64 arena_vm_start;
u8 *image_ptr;
u8 *ro_image_ptr;
@@ -1611,6 +1659,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
prog = tmp;
}
+ arena_vm_start = bpf_arena_get_kern_vm_start(prog->aux->arena);
jit_data = prog->aux->jit_data;
if (!jit_data) {
jit_data = kzalloc(sizeof(*jit_data), GFP_KERNEL);
@@ -1648,7 +1697,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
* BPF line info needs ctx->offset[i] to be the offset of
* instruction[i] in jited image, so build prologue first.
*/
- if (build_prologue(&ctx, was_classic, prog->aux->exception_cb)) {
+ if (build_prologue(&ctx, was_classic, prog->aux->exception_cb,
+ arena_vm_start)) {
prog = orig_prog;
goto out_off;
}
@@ -1696,7 +1746,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
ctx.idx = 0;
ctx.exentry_idx = 0;
- build_prologue(&ctx, was_classic, prog->aux->exception_cb);
+ build_prologue(&ctx, was_classic, prog->aux->exception_cb, arena_vm_start);
if (build_body(&ctx, extra_pass)) {
prog = orig_prog;
--
2.40.1