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net: filter: make JITs zero A for SKF_AD_ALU_XOR_X

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The SKF_AD_ALU_XOR_X ancillary is not like the other ancillary data
instructions since it XORs A with X while all the others replace A with
some loaded value.  All the BPF JITs fail to clear A if this is used as
the first instruction in a filter.  This was found using american fuzzy
lop.

Add a helper to determine if A needs to be cleared given the first
instruction in a filter, and use this in the JITs.  Except for ARM, the
rest have only been compile-tested.

Fixes: 3480593131 ("net: filter: get rid of BPF_S_* enum")
Signed-off-by: Rabin Vincent <rabin@rab.in>
Acked-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:
Rabin Vincent
2016-01-05 16:23:07 +01:00
committed by David S. Miller
parent ff62198553
commit 55795ef546
5 changed files with 25 additions and 56 deletions
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16
arch/mips/net/bpf_jit.c
View File

@@ -521,19 +521,6 @@ static inline u16 align_sp(unsigned int num)
return num;
}
static bool is_load_to_a(u16 inst)
{
switch (inst) {
case BPF_LD | BPF_W | BPF_LEN:
case BPF_LD | BPF_W | BPF_ABS:
case BPF_LD | BPF_H | BPF_ABS:
case BPF_LD | BPF_B | BPF_ABS:
return true;
default:
return false;
}
}
static void save_bpf_jit_regs(struct jit_ctx *ctx, unsigned offset)
{
int i = 0, real_off = 0;
@@ -614,7 +601,6 @@ static unsigned int get_stack_depth(struct jit_ctx *ctx)
static void build_prologue(struct jit_ctx *ctx)
{
u16 first_inst = ctx->skf->insns[0].code;
int sp_off;
/* Calculate the total offset for the stack pointer */
@@ -641,7 +627,7 @@ static void build_prologue(struct jit_ctx *ctx)
emit_jit_reg_move(r_X, r_zero, ctx);
/* Do not leak kernel data to userspace */
if ((first_inst != (BPF_RET | BPF_K)) && !(is_load_to_a(first_inst)))
if (bpf_needs_clear_a(&ctx->skf->insns[0]))
emit_jit_reg_move(r_A, r_zero, ctx);
}