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net: filter: make JITs zero A for SKF_AD_ALU_XOR_X 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
arch/arm/net/bpf_jit_32.c
View File

@ -187,19 +187,6 @@ static inline int mem_words_used(struct jit_ctx *ctx)
return fls(ctx->seen & SEEN_MEM);
}
static inline 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 jit_fill_hole(void *area, unsigned int size)
{
u32 *ptr;
@ -211,7 +198,6 @@ static void jit_fill_hole(void *area, unsigned int size)
static void build_prologue(struct jit_ctx *ctx)
{
u16 reg_set = saved_regs(ctx);
u16 first_inst = ctx->skf->insns[0].code;
u16 off;
#ifdef CONFIG_FRAME_POINTER
@ -241,7 +227,7 @@ static void build_prologue(struct jit_ctx *ctx)
emit(ARM_MOV_I(r_X, 0), 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(ARM_MOV_I(r_A, 0), ctx);
/* stack space for the BPF_MEM words */

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);
}

11
arch/powerpc/net/bpf_jit_comp.c
View File

@ -78,18 +78,9 @@ static void bpf_jit_build_prologue(struct bpf_prog *fp, u32 *image,
PPC_LI(r_X, 0);
}
switch (filter[0].code) {
case BPF_RET | BPF_K:
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:
/* first instruction sets A register (or is RET 'constant') */
break;
default:
/* make sure we dont leak kernel information to user */
if (bpf_needs_clear_a(&filter[0]))
PPC_LI(r_A, 0);
}
}
static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)

17
arch/sparc/net/bpf_jit_comp.c
View File

@ -420,22 +420,9 @@ void bpf_jit_compile(struct bpf_prog *fp)
}
emit_reg_move(O7, r_saved_O7);
switch (filter[0].code) {
case BPF_RET | BPF_K:
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:
/* The first instruction sets the A register (or is
* a "RET 'constant'")
*/
break;
default:
/* Make sure we dont leak kernel information to the
* user.
*/
/* Make sure we dont leak kernel information to the user. */
if (bpf_needs_clear_a(&filter[0]))
emit_clear(r_A); /* A = 0 */
}
for (i = 0; i < flen; i++) {
unsigned int K = filter[i].k;

19
include/linux/filter.h
View File

@ -493,6 +493,25 @@ static inline void bpf_jit_free(struct bpf_prog *fp)
#define BPF_ANC BIT(15)
static inline bool bpf_needs_clear_a(const struct sock_filter *first)
{
switch (first->code) {
case BPF_RET | BPF_K:
case BPF_LD | BPF_W | BPF_LEN:
return false;
case BPF_LD | BPF_W | BPF_ABS:
case BPF_LD | BPF_H | BPF_ABS:
case BPF_LD | BPF_B | BPF_ABS:
if (first->k == SKF_AD_OFF + SKF_AD_ALU_XOR_X)
return true;
return false;
default:
return true;
}
}
static inline u16 bpf_anc_helper(const struct sock_filter *ftest)
{
BUG_ON(ftest->code & BPF_ANC);