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bpf: Add x86-64 JIT support for PROBE_MEM32 pseudo instructions. 

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_MEM has to check that the address is in the kernel range with
  src_reg + insn->off >= TASK_SIZE_MAX + PAGE_SIZE check
- PROBE_MEM doesn't support store
- PROBE_MEM32 relies on the verifier to clear upper 32-bit in the register
- PROBE_MEM32 adds 64-bit kern_vm_start address (which is stored in %r12 in the prologue)
  Due to bpf_arena constructions such %r12 + %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.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20240308010812.89848-4-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2024-03-07 17:08:01 -08:00 committed by Andrii Nakryiko
parent 667a86ad9b
commit 2fe99eb0cc
3 changed files with 194 additions and 1 deletions
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191
arch/x86/net/bpf_jit_comp.c
View File

@ -113,6 +113,7 @@ static int bpf_size_to_x86_bytes(int bpf_size)
/* Pick a register outside of BPF range for JIT internal work */
#define AUX_REG (MAX_BPF_JIT_REG + 1)
#define X86_REG_R9 (MAX_BPF_JIT_REG + 2)
#define X86_REG_R12 (MAX_BPF_JIT_REG + 3)
/*
* The following table maps BPF registers to x86-64 registers.
@ -139,6 +140,7 @@ static const int reg2hex[] = {
[BPF_REG_AX] = 2, /* R10 temp register */
[AUX_REG] = 3, /* R11 temp register */
[X86_REG_R9] = 1, /* R9 register, 6th function argument */
[X86_REG_R12] = 4, /* R12 callee saved */
};
static const int reg2pt_regs[] = {
@ -167,6 +169,7 @@ static bool is_ereg(u32 reg)
BIT(BPF_REG_8) |
BIT(BPF_REG_9) |
BIT(X86_REG_R9) |
BIT(X86_REG_R12) |
BIT(BPF_REG_AX));
}
@ -205,6 +208,17 @@ static u8 add_2mod(u8 byte, u32 r1, u32 r2)
return byte;
}
static u8 add_3mod(u8 byte, u32 r1, u32 r2, u32 index)
{
if (is_ereg(r1))
byte |= 1;
if (is_ereg(index))
byte |= 2;
if (is_ereg(r2))
byte |= 4;
return byte;
}
/* Encode 'dst_reg' register into x86-64 opcode 'byte' */
static u8 add_1reg(u8 byte, u32 dst_reg)
{
@ -645,6 +659,8 @@ static void emit_bpf_tail_call_indirect(struct bpf_prog *bpf_prog,
pop_r12(&prog);
} else {
pop_callee_regs(&prog, callee_regs_used);
if (bpf_arena_get_kern_vm_start(bpf_prog->aux->arena))
pop_r12(&prog);
}
EMIT1(0x58); /* pop rax */
@ -704,6 +720,8 @@ static void emit_bpf_tail_call_direct(struct bpf_prog *bpf_prog,
pop_r12(&prog);
} else {
pop_callee_regs(&prog, callee_regs_used);
if (bpf_arena_get_kern_vm_start(bpf_prog->aux->arena))
pop_r12(&prog);
}
EMIT1(0x58); /* pop rax */
@ -887,6 +905,18 @@ static void emit_insn_suffix(u8 **pprog, u32 ptr_reg, u32 val_reg, int off)
*pprog = prog;
}
static void emit_insn_suffix_SIB(u8 **pprog, u32 ptr_reg, u32 val_reg, u32 index_reg, int off)
{
u8 *prog = *pprog;
if (is_imm8(off)) {
EMIT3(add_2reg(0x44, BPF_REG_0, val_reg), add_2reg(0, ptr_reg, index_reg) /* SIB */, off);
} else {
EMIT2_off32(add_2reg(0x84, BPF_REG_0, val_reg), add_2reg(0, ptr_reg, index_reg) /* SIB */, off);
}
*pprog = prog;
}
/*
* Emit a REX byte if it will be necessary to address these registers
*/
@ -968,6 +998,37 @@ static void emit_ldsx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
*pprog = prog;
}
static void emit_ldx_index(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, u32 index_reg, int off)
{
u8 *prog = *pprog;
switch (size) {
case BPF_B:
/* movzx rax, byte ptr [rax + r12 + off] */
EMIT3(add_3mod(0x40, src_reg, dst_reg, index_reg), 0x0F, 0xB6);
break;
case BPF_H:
/* movzx rax, word ptr [rax + r12 + off] */
EMIT3(add_3mod(0x40, src_reg, dst_reg, index_reg), 0x0F, 0xB7);
break;
case BPF_W:
/* mov eax, dword ptr [rax + r12 + off] */
EMIT2(add_3mod(0x40, src_reg, dst_reg, index_reg), 0x8B);
break;
case BPF_DW:
/* mov rax, qword ptr [rax + r12 + off] */
EMIT2(add_3mod(0x48, src_reg, dst_reg, index_reg), 0x8B);
break;
}
emit_insn_suffix_SIB(&prog, src_reg, dst_reg, index_reg, off);
*pprog = prog;
}
static void emit_ldx_r12(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
{
emit_ldx_index(pprog, size, dst_reg, src_reg, X86_REG_R12, off);
}
/* STX: *(u8*)(dst_reg + off) = src_reg */
static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
{
@ -1002,6 +1063,71 @@ static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
*pprog = prog;
}
/* STX: *(u8*)(dst_reg + index_reg + off) = src_reg */
static void emit_stx_index(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, u32 index_reg, int off)
{
u8 *prog = *pprog;
switch (size) {
case BPF_B:
/* mov byte ptr [rax + r12 + off], al */
EMIT2(add_3mod(0x40, dst_reg, src_reg, index_reg), 0x88);
break;
case BPF_H:
/* mov word ptr [rax + r12 + off], ax */
EMIT3(0x66, add_3mod(0x40, dst_reg, src_reg, index_reg), 0x89);
break;
case BPF_W:
/* mov dword ptr [rax + r12 + 1], eax */
EMIT2(add_3mod(0x40, dst_reg, src_reg, index_reg), 0x89);
break;
case BPF_DW:
/* mov qword ptr [rax + r12 + 1], rax */
EMIT2(add_3mod(0x48, dst_reg, src_reg, index_reg), 0x89);
break;
}
emit_insn_suffix_SIB(&prog, dst_reg, src_reg, index_reg, off);
*pprog = prog;
}
static void emit_stx_r12(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
{
emit_stx_index(pprog, size, dst_reg, src_reg, X86_REG_R12, off);
}
/* ST: *(u8*)(dst_reg + index_reg + off) = imm32 */
static void emit_st_index(u8 **pprog, u32 size, u32 dst_reg, u32 index_reg, int off, int imm)
{
u8 *prog = *pprog;
switch (size) {
case BPF_B:
/* mov byte ptr [rax + r12 + off], imm8 */
EMIT2(add_3mod(0x40, dst_reg, 0, index_reg), 0xC6);
break;
case BPF_H:
/* mov word ptr [rax + r12 + off], imm16 */
EMIT3(0x66, add_3mod(0x40, dst_reg, 0, index_reg), 0xC7);
break;
case BPF_W:
/* mov dword ptr [rax + r12 + 1], imm32 */
EMIT2(add_3mod(0x40, dst_reg, 0, index_reg), 0xC7);
break;
case BPF_DW:
/* mov qword ptr [rax + r12 + 1], imm32 */
EMIT2(add_3mod(0x48, dst_reg, 0, index_reg), 0xC7);
break;
}
emit_insn_suffix_SIB(&prog, dst_reg, 0, index_reg, off);
EMIT(imm, bpf_size_to_x86_bytes(size));
*pprog = prog;
}
static void emit_st_r12(u8 **pprog, u32 size, u32 dst_reg, int off, int imm)
{
emit_st_index(pprog, size, dst_reg, X86_REG_R12, off, imm);
}
static int emit_atomic(u8 **pprog, u8 atomic_op,
u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size)
{
@ -1043,12 +1169,15 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
return 0;
}
#define DONT_CLEAR 1
bool ex_handler_bpf(const struct exception_table_entry *x, struct pt_regs *regs)
{
u32 reg = x->fixup >> 8;
/* jump over faulting load and clear dest register */
*(unsigned long *)((void *)regs + reg) = 0;
if (reg != DONT_CLEAR)
*(unsigned long *)((void *)regs + reg) = 0;
regs->ip += x->fixup & 0xff;
return true;
}
@ -1147,11 +1276,14 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
bool tail_call_seen = false;
bool seen_exit = false;
u8 temp[BPF_MAX_INSN_SIZE + BPF_INSN_SAFETY];
u64 arena_vm_start;
int i, excnt = 0;
int ilen, proglen = 0;
u8 *prog = temp;
int err;
arena_vm_start = bpf_arena_get_kern_vm_start(bpf_prog->aux->arena);
detect_reg_usage(insn, insn_cnt, callee_regs_used,
&tail_call_seen);
@ -1172,8 +1304,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
push_r12(&prog);
push_callee_regs(&prog, all_callee_regs_used);
} else {
if (arena_vm_start)
push_r12(&prog);
push_callee_regs(&prog, callee_regs_used);
}
if (arena_vm_start)
emit_mov_imm64(&prog, X86_REG_R12,
arena_vm_start >> 32, (u32) arena_vm_start);
ilen = prog - temp;
if (rw_image)
@ -1564,6 +1701,56 @@ st: if (is_imm8(insn->off))
emit_stx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off);
break;
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:
start_of_ldx = prog;
emit_st_r12(&prog, BPF_SIZE(insn->code), dst_reg, insn->off, insn->imm);
goto populate_extable;
/* LDX: dst_reg = *(u8*)(src_reg + r12 + off) */
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:
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:
start_of_ldx = prog;
if (BPF_CLASS(insn->code) == BPF_LDX)
emit_ldx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off);
else
emit_stx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off);
populate_extable:
{
struct exception_table_entry *ex;
u8 *_insn = image + proglen + (start_of_ldx - temp);
s64 delta;
if (!bpf_prog->aux->extable)
break;
if (excnt >= bpf_prog->aux->num_exentries) {
pr_err("mem32 extable bug\n");
return -EFAULT;
}
ex = &bpf_prog->aux->extable[excnt++];
delta = _insn - (u8 *)&ex->insn;
/* switch ex to rw buffer for writes */
ex = (void *)rw_image + ((void *)ex - (void *)image);
ex->insn = delta;
ex->data = EX_TYPE_BPF;
ex->fixup = (prog - start_of_ldx) |
((BPF_CLASS(insn->code) == BPF_LDX ? reg2pt_regs[dst_reg] : DONT_CLEAR) << 8);
}
break;
/* LDX: dst_reg = *(u8*)(src_reg + off) */
case BPF_LDX | BPF_MEM | BPF_B:
case BPF_LDX | BPF_PROBE_MEM | BPF_B:
@ -2036,6 +2223,8 @@ emit_jmp:
pop_r12(&prog);
} else {
pop_callee_regs(&prog, callee_regs_used);
if (arena_vm_start)
pop_r12(&prog);
}
EMIT1(0xC9); /* leave */
emit_return(&prog, image + addrs[i - 1] + (prog - temp));

1
include/linux/bpf.h
View File

@ -1458,6 +1458,7 @@ struct bpf_prog_aux {
bool xdp_has_frags;
bool exception_cb;
bool exception_boundary;
struct bpf_arena *arena;
/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
const struct btf_type *attach_func_proto;
/* function name for valid attach_btf_id */

3
include/linux/filter.h
View File

@ -72,6 +72,9 @@ struct ctl_table_header;
/* unused opcode to mark special ldsx instruction. Same as BPF_IND */
#define BPF_PROBE_MEMSX 0x40
/* unused opcode to mark special load instruction. Same as BPF_MSH */
#define BPF_PROBE_MEM32 0xa0
/* unused opcode to mark call to interpreter with arguments */
#define BPF_CALL_ARGS 0xe0