[PATCH] net: filter: make JITs zero A for SKF_AD_ALU_XOR_X
Rabin Vincent
rabin at rab.in
Tue Jan 5 07:23:07 PST 2016
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: 3480593131e0 ("net: filter: get rid of BPF_S_* enum")
Signed-off-by: Rabin Vincent <rabin at rab.in>
---
arch/arm/net/bpf_jit_32.c | 16 +---------------
arch/mips/net/bpf_jit.c | 16 +---------------
arch/powerpc/net/bpf_jit_comp.c | 13 ++-----------
arch/sparc/net/bpf_jit_comp.c | 17 ++---------------
include/linux/filter.h | 19 +++++++++++++++++++
5 files changed, 25 insertions(+), 56 deletions(-)
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 591f9db3bf40..e153eb065fe4 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -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 */
diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 77cb27309db2..1a8c96035716 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c
@@ -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);
}
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 04782164ee67..2d66a8446198 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -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 */
+ /* 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)
diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
index 22564f5f2364..3e6e05a7c4c2 100644
--- a/arch/sparc/net/bpf_jit_comp.c
+++ b/arch/sparc/net/bpf_jit_comp.c
@@ -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;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 4165e9ac9e36..5972ffe5719a 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -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);
--
2.6.4
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