Commit 02ab695b authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

net: filter: add "load 64-bit immediate" eBPF instruction 



add BPF_LD_IMM64 instruction to load 64-bit immediate value into a register.
All previous instructions were 8-byte. This is first 16-byte instruction.
Two consecutive 'struct bpf_insn' blocks are interpreted as single instruction:
insn[0].code = BPF_LD | BPF_DW | BPF_IMM
insn[0].dst_reg = destination register
insn[0].imm = lower 32-bit
insn[1].code = 0
insn[1].imm = upper 32-bit
All unused fields must be zero.

Classic BPF has similar instruction: BPF_LD | BPF_W | BPF_IMM
which loads 32-bit immediate value into a register.

x64 JITs it as single 'movabsq %rax, imm64'
arm64 may JIT as sequence of four 'movk x0, #imm16, lsl #shift' insn

Note that old eBPF programs are binary compatible with new interpreter.

It helps eBPF programs load 64-bit constant into a register with one
instruction instead of using two registers and 4 instructions:
BPF_MOV32_IMM(R1, imm32)
BPF_ALU64_IMM(BPF_LSH, R1, 32)
BPF_MOV32_IMM(R2, imm32)
BPF_ALU64_REG(BPF_OR, R1, R2)

User space generated programs will use this instruction to load constants only.

To tell kernel that user space needs a pointer the _pseudo_ variant of
this instruction may be added later, which will use extra bits of encoding
to indicate what type of pointer user space is asking kernel to provide.
For example 'off' or 'src_reg' fields can be used for such purpose.
src_reg = 1 could mean that user space is asking kernel to validate and
load in-kernel map pointer.
src_reg = 2 could mean that user space needs readonly data section pointer
src_reg = 3 could mean that user space needs a pointer to per-cpu local data
All such future pseudo instructions will not be carrying the actual pointer
as part of the instruction, but rather will be treated as a request to kernel
to provide one. The kernel will verify the request_for_a_pointer, then
will drop _pseudo_ marking and will store actual internal pointer inside
the instruction, so the end result is the interpreter and JITs never
see pseudo BPF_LD_IMM64 insns and only operate on generic BPF_LD_IMM64 that
loads 64-bit immediate into a register. User space never operates on direct
pointers and verifier can easily recognize request_for_pointer vs other
instructions.

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5b4c3145

Documentation/networking/filter.txt

+7 −1
Original line number Diff line number Diff line
@@ -951,7 +951,7 @@ Size modifier is one of ... 


Mode modifier is one of:



  BPF_IMM  0x00  /* classic BPF only, reserved in eBPF */

  BPF_IMM  0x00  /* used for 32-bit mov in classic BPF and 64-bit in eBPF */

  BPF_ABS  0x20

  BPF_IND  0x40

  BPF_MEM  0x60
@@ -995,6 +995,12 @@ BPF_XADD | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg 
Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. Note that 1 and

2 byte atomic increments are not supported.



eBPF has one 16-byte instruction: BPF_LD | BPF_DW | BPF_IMM which consists

of two consecutive 'struct bpf_insn' 8-byte blocks and interpreted as single

instruction that loads 64-bit immediate value into a dst_reg.

Classic BPF has similar instruction: BPF_LD | BPF_W | BPF_IMM which loads

32-bit immediate value into a register.



Testing

-------

arch/x86/net/bpf_jit_comp.c

+17 −0
Original line number Diff line number Diff line
@@ -393,6 +393,23 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, 
			EMIT1_off32(add_1reg(0xB8, dst_reg), imm32);

			break;



		case BPF_LD | BPF_IMM | BPF_DW:

			if (insn[1].code != 0 || insn[1].src_reg != 0 ||

			    insn[1].dst_reg != 0 || insn[1].off != 0) {

				/* verifier must catch invalid insns */

				pr_err("invalid BPF_LD_IMM64 insn\n");

				return -EINVAL;

			}



			/* movabsq %rax, imm64 */

			EMIT2(add_1mod(0x48, dst_reg), add_1reg(0xB8, dst_reg));

			EMIT(insn[0].imm, 4);

			EMIT(insn[1].imm, 4);



			insn++;

			i++;

			break;



			/* dst %= src, dst /= src, dst %= imm32, dst /= imm32 */

		case BPF_ALU | BPF_MOD | BPF_X:

		case BPF_ALU | BPF_DIV | BPF_X:

include/linux/filter.h

+18 −0
Original line number Diff line number Diff line
@@ -166,6 +166,24 @@ enum { 
		.off   = 0,					\

		.imm   = IMM })



/* BPF_LD_IMM64 macro encodes single 'load 64-bit immediate' insn */

#define BPF_LD_IMM64(DST, IMM)					\

	BPF_LD_IMM64_RAW(DST, 0, IMM)



#define BPF_LD_IMM64_RAW(DST, SRC, IMM)				\

	((struct bpf_insn) {					\

		.code  = BPF_LD | BPF_DW | BPF_IMM,		\

		.dst_reg = DST,					\

		.src_reg = SRC,					\

		.off   = 0,					\

		.imm   = (__u32) (IMM) }),			\

	((struct bpf_insn) {					\

		.code  = 0, /* zero is reserved opcode */	\

		.dst_reg = 0,					\

		.src_reg = 0,					\

		.off   = 0,					\

		.imm   = ((__u64) (IMM)) >> 32 })



/* Short form of mov based on type, BPF_X: dst_reg = src_reg, BPF_K: dst_reg = imm32 */



#define BPF_MOV64_RAW(TYPE, DST, SRC, IMM)			\

kernel/bpf/core.c

+5 −0
Original line number Diff line number Diff line
@@ -242,6 +242,7 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn) 
		[BPF_LD | BPF_IND | BPF_W] = &&LD_IND_W,

		[BPF_LD | BPF_IND | BPF_H] = &&LD_IND_H,

		[BPF_LD | BPF_IND | BPF_B] = &&LD_IND_B,

		[BPF_LD | BPF_IMM | BPF_DW] = &&LD_IMM_DW,

	};

	void *ptr;

	int off;
@@ -301,6 +302,10 @@ select_insn: 
	ALU64_MOV_K:

		DST = IMM;

		CONT;

	LD_IMM_DW:

		DST = (u64) (u32) insn[0].imm | ((u64) (u32) insn[1].imm) << 32;

		insn++;

		CONT;

	ALU64_ARSH_X:

		(*(s64 *) &DST) >>= SRC;

		CONT;

lib/test_bpf.c

+21 −0
Original line number Diff line number Diff line
@@ -1735,6 +1735,27 @@ static struct bpf_test tests[] = { 
		{ },

		{ { 1, 0 } },

	},

	{

		"load 64-bit immediate",

		.u.insns_int = {

			BPF_LD_IMM64(R1, 0x567800001234L),

			BPF_MOV64_REG(R2, R1),

			BPF_MOV64_REG(R3, R2),

			BPF_ALU64_IMM(BPF_RSH, R2, 32),

			BPF_ALU64_IMM(BPF_LSH, R3, 32),

			BPF_ALU64_IMM(BPF_RSH, R3, 32),

			BPF_ALU64_IMM(BPF_MOV, R0, 0),

			BPF_JMP_IMM(BPF_JEQ, R2, 0x5678, 1),

			BPF_EXIT_INSN(),

			BPF_JMP_IMM(BPF_JEQ, R3, 0x1234, 1),

			BPF_EXIT_INSN(),

			BPF_ALU64_IMM(BPF_MOV, R0, 1),

			BPF_EXIT_INSN(),

		},

		INTERNAL,

		{ },

		{ { 0, 1 } }

	},

};



static struct net_device dev;

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