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bpf, x86: add support for constant blinding

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This patch adds recently added constant blinding helpers into the
x86 eBPF JIT. In the bpf_int_jit_compile() path, requirements are
to utilize bpf_jit_blind_constants()/bpf_jit_prog_release_other()
pair for rewriting the program into a blinded one, and to map the
BPF_REG_AX register to a CPU register. The mapping of BPF_REG_AX
is at non-callee saved register r10, and thus shared with cached
skb->data used for ld_abs/ind and not in every program type needed.
When blinding is not used, there's zero additional overhead in the
generated image.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Daniel Borkmann 2016-05-13 19:08:33 +02:00 committed by David S. Miller
parent 4f3446bb80
commit 959a757916
1 changed files with 53 additions and 13 deletions
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66
arch/x86/net/bpf_jit_comp.c
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@ -110,11 +110,16 @@ static void bpf_flush_icache(void *start, void *end)
((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
/* pick a register outside of BPF range for JIT internal work */
#define AUX_REG (MAX_BPF_REG + 1)
#define AUX_REG (MAX_BPF_JIT_REG + 1)
/* the following table maps BPF registers to x64 registers.
* x64 register r12 is unused, since if used as base address register
* in load/store instructions, it always needs an extra byte of encoding
/* The following table maps BPF registers to x64 registers.
*
* x64 register r12 is unused, since if used as base address
* register in load/store instructions, it always needs an
* extra byte of encoding and is callee saved.
*
* r9 caches skb->len - skb->data_len
* r10 caches skb->data, and used for blinding (if enabled)
*/
static const int reg2hex[] = {
[BPF_REG_0] = 0, /* rax */
@ -128,6 +133,7 @@ static const int reg2hex[] = {
[BPF_REG_8] = 6, /* r14 callee saved */
[BPF_REG_9] = 7, /* r15 callee saved */
[BPF_REG_FP] = 5, /* rbp readonly */
[BPF_REG_AX] = 2, /* r10 temp register */
[AUX_REG] = 3, /* r11 temp register */
};
@ -141,7 +147,8 @@ static bool is_ereg(u32 reg)
BIT(AUX_REG) |
BIT(BPF_REG_7) |
BIT(BPF_REG_8) |
BIT(BPF_REG_9));
BIT(BPF_REG_9) |
BIT(BPF_REG_AX));
}
/* add modifiers if 'reg' maps to x64 registers r8..r15 */
@ -182,6 +189,7 @@ static void jit_fill_hole(void *area, unsigned int size)
struct jit_context {
int cleanup_addr; /* epilogue code offset */
bool seen_ld_abs;
bool seen_ax_reg;
};
/* maximum number of bytes emitted while JITing one eBPF insn */
@ -345,6 +353,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
struct bpf_insn *insn = bpf_prog->insnsi;
int insn_cnt = bpf_prog->len;
bool seen_ld_abs = ctx->seen_ld_abs | (oldproglen == 0);
bool seen_ax_reg = ctx->seen_ax_reg | (oldproglen == 0);
bool seen_exit = false;
u8 temp[BPF_MAX_INSN_SIZE + BPF_INSN_SAFETY];
int i, cnt = 0;
@ -367,6 +376,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
int ilen;
u8 *func;
if (dst_reg == BPF_REG_AX || src_reg == BPF_REG_AX)
ctx->seen_ax_reg = seen_ax_reg = true;
switch (insn->code) {
/* ALU */
case BPF_ALU | BPF_ADD | BPF_X:
@ -1002,6 +1014,10 @@ common_load:
* sk_load_* helpers also use %r10 and %r9d.
* See bpf_jit.S
*/
if (seen_ax_reg)
/* r10 = skb->data, mov %r10, off32(%rbx) */
EMIT3_off32(0x4c, 0x8b, 0x93,
offsetof(struct sk_buff, data));
EMIT1_off32(0xE8, jmp_offset); /* call */
break;
@ -1076,19 +1092,34 @@ void bpf_jit_compile(struct bpf_prog *prog)
struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
{
struct bpf_binary_header *header = NULL;
struct bpf_prog *tmp, *orig_prog = prog;
int proglen, oldproglen = 0;
struct jit_context ctx = {};
bool tmp_blinded = false;
u8 *image = NULL;
int *addrs;
int pass;
int i;
if (!bpf_jit_enable)
return prog;
return orig_prog;
tmp = bpf_jit_blind_constants(prog);
/* If blinding was requested and we failed during blinding,
* we must fall back to the interpreter.
*/
if (IS_ERR(tmp))
return orig_prog;
if (tmp != prog) {
tmp_blinded = true;
prog = tmp;
}
addrs = kmalloc(prog->len * sizeof(*addrs), GFP_KERNEL);
if (!addrs)
return prog;
if (!addrs) {
prog = orig_prog;
goto out;
}
/* Before first pass, make a rough estimation of addrs[]
* each bpf instruction is translated to less than 64 bytes
@ -1110,21 +1141,25 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
image = NULL;
if (header)
bpf_jit_binary_free(header);
goto out;
prog = orig_prog;
goto out_addrs;
}
if (image) {
if (proglen != oldproglen) {
pr_err("bpf_jit: proglen=%d != oldproglen=%d\n",
proglen, oldproglen);
goto out;
prog = orig_prog;
goto out_addrs;
}
break;
}
if (proglen == oldproglen) {
header = bpf_jit_binary_alloc(proglen, &image,
1, jit_fill_hole);
if (!header)
goto out;
if (!header) {
prog = orig_prog;
goto out_addrs;
}
}
oldproglen = proglen;
}
@ -1138,8 +1173,13 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
prog->bpf_func = (void *)image;
prog->jited = 1;
}
out:
out_addrs:
kfree(addrs);
out:
if (tmp_blinded)
bpf_jit_prog_release_other(prog, prog == orig_prog ?
tmp : orig_prog);
return prog;
}