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: 3480593131e0 ("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>

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 591f9db3bf4048a4d727f195e4e2fb95e4ca06c4..e153eb065fe453a03c5b4f1b4abacf8c57a460dd 100644 (file)
--- 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 77cb27309db27f781ec9862037074d39e928401a..1a8c96035716a2dfb76f724b6190b33954bee8c8 100644 (file)
--- 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 04782164ee67d8a570bcb4b4ee166dc6809753de..2d66a8446198dfcf48849c61a561cf7527f79e56 100644 (file)
--- 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 22564f5f23647a6f54752052091d2c74c194bccf..3e6e05a7c4c22b297861eb82871d92b7217cffee 100644 (file)
--- 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 4165e9ac9e36aa82735f40a790e25e0b7218c95b..5972ffe5719a4e14012328035450759c12f43bec 100644 (file)
--- 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);