Re: [bpf/tools] cd17d77705: kernel_selftests.bpf.test_sock_addr.sh.fail

From: Andrii Nakryiko
Date: Thu Jun 27 2019 - 22:22:21 EST

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On Thu, Jun 27, 2019 at 10:29 AM Stanislav Fomichev <sdf@xxxxxxxxxxx> wrote:
>
> On 06/27, Stanislav Fomichev wrote:
> > On 06/27, kernel test robot wrote:
> > > FYI, we noticed the following commit (built with gcc-7):
> > >
> > > commit: cd17d77705780e2270937fb3cbd2b985adab3edc ("bpf/tools: sync bpf.h")
> > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> > >
> > > in testcase: kernel_selftests
> > > with following parameters:
> > >
> > > group: kselftests-00
> > >
> > > test-description: The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel.
> > > test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
> > >
> > >
> > > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
> > >
> > > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> > >
> > > # ; int connect_v6_prog(struct bpf_sock_addr *ctx)
> > > # 0: (bf) r6 = r1
> > > # 1: (18) r1 = 0x100000000000000
> > > # ; tuple.ipv6.daddr[0] = bpf_htonl(DST_REWRITE_IP6_0);
> > > # 3: (7b) *(u64 *)(r10 -16) = r1
> > > # 4: (b7) r1 = 169476096
> > > # ; memset(&tuple.ipv6.sport, 0, sizeof(tuple.ipv6.sport));
> > > # 5: (63) *(u32 *)(r10 -8) = r1
> > > # 6: (b7) r7 = 0
> > > # ; tuple.ipv6.daddr[0] = bpf_htonl(DST_REWRITE_IP6_0);
> > > # 7: (7b) *(u64 *)(r10 -24) = r7
> > > # 8: (7b) *(u64 *)(r10 -32) = r7
> > > # 9: (7b) *(u64 *)(r10 -40) = r7
> > > # ; if (ctx->type != SOCK_STREAM && ctx->type != SOCK_DGRAM)
> > > # 10: (61) r1 = *(u32 *)(r6 +32)
> > > # ; if (ctx->type != SOCK_STREAM && ctx->type != SOCK_DGRAM)
> > > # 11: (bf) r2 = r1
> > > # 12: (07) r2 += -1
> > > # 13: (67) r2 <<= 32
> > > # 14: (77) r2 >>= 32
> > > # 15: (25) if r2 > 0x1 goto pc+33
> > > # R1=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv(id=0,umax_value=1,var_off=(0x0; 0x1)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=00000000 fp-32=00000000 fp-40=00000000
> > > # ; else if (ctx->type == SOCK_STREAM)
> > > # 16: (55) if r1 != 0x1 goto pc+8
> > > # R1=inv1 R2=inv(id=0,umax_value=1,var_off=(0x0; 0x1)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=00000000 fp-32=00000000 fp-40=00000000
> > > # 17: (bf) r2 = r10
> > > # ; sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof(tuple.ipv6),
> > > # 18: (07) r2 += -40
> > > # 19: (bf) r1 = r6
> > > # 20: (b7) r3 = 36
> > > # 21: (b7) r4 = -1
> > > # 22: (b7) r5 = 0
> > > # 23: (85) call bpf_sk_lookup_tcp#84
> > > # 24: (05) goto pc+7
> > > # ; if (!sk)
> > > # 32: (15) if r0 == 0x0 goto pc+16
> > > # R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; if (sk->src_ip6[0] != tuple.ipv6.daddr[0] ||
> > > # 33: (61) r1 = *(u32 *)(r0 +28)
> > > # ; if (sk->src_ip6[0] != tuple.ipv6.daddr[0] ||
> > > # 34: (61) r2 = *(u32 *)(r10 -24)
> > > # ; if (sk->src_ip6[0] != tuple.ipv6.daddr[0] ||
> > > # 35: (5d) if r1 != r2 goto pc+11
> > > # R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R1=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; sk->src_ip6[1] != tuple.ipv6.daddr[1] ||
> > > # 36: (61) r1 = *(u32 *)(r0 +32)
> > > # ; sk->src_ip6[1] != tuple.ipv6.daddr[1] ||
> > > # 37: (61) r2 = *(u32 *)(r10 -20)
> > > # ; sk->src_ip6[1] != tuple.ipv6.daddr[1] ||
> > > # 38: (5d) if r1 != r2 goto pc+8
> > > # R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R1=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; sk->src_ip6[2] != tuple.ipv6.daddr[2] ||
> > > # 39: (61) r1 = *(u32 *)(r0 +36)
> > > # ; sk->src_ip6[2] != tuple.ipv6.daddr[2] ||
> > > # 40: (61) r2 = *(u32 *)(r10 -16)
> > > # ; sk->src_ip6[2] != tuple.ipv6.daddr[2] ||
> > > # 41: (5d) if r1 != r2 goto pc+5
> > > # R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R1=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; sk->src_ip6[3] != tuple.ipv6.daddr[3] ||
> > > # 42: (61) r1 = *(u32 *)(r0 +40)
> > > # ; sk->src_ip6[3] != tuple.ipv6.daddr[3] ||
> > > # 43: (61) r2 = *(u32 *)(r10 -12)
> > > # ; sk->src_ip6[3] != tuple.ipv6.daddr[3] ||
> > > # 44: (5d) if r1 != r2 goto pc+2
> > > # R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R1=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; sk->src_port != DST_REWRITE_PORT6) {
> > > # 45: (61) r1 = *(u32 *)(r0 +44)
> > > # ; if (sk->src_ip6[0] != tuple.ipv6.daddr[0] ||
> > > # 46: (15) if r1 == 0x1a0a goto pc+4
> > > # R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R1=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; bpf_sk_release(sk);
> > > # 47: (bf) r1 = r0
> > > # 48: (85) call bpf_sk_release#86
> > > # ; }
> > > # 49: (bf) r0 = r7
> > > # 50: (95) exit
> > > #
> > > # from 46 to 51: R0=sock(id=0,ref_obj_id=2,off=0,imm=0) R1=inv6666 R2=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R6=ctx(id=0,off=0,imm=0) R7=inv0 R10=fp0,call_-1 fp-8=????mmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm refs=2
> > > # ; bpf_sk_release(sk);
> > > # 51: (bf) r1 = r0
> > > # 52: (85) call bpf_sk_release#86
> > > # 53: (b7) r1 = 2586
> > > # ; ctx->user_port = bpf_htons(DST_REWRITE_PORT6);
> > > # 54: (63) *(u32 *)(r6 +24) = r1
> > > # 55: (18) r1 = 0x100000000000000
> > > # ; ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_2);
> > > # 57: (7b) *(u64 *)(r6 +16) = r1
> > > # invalid bpf_context access off=16 size=8
> > This looks like clang doing single u64 write for user_ip6[2] and
> > user_ip6[3] instead of two u32. I don't think we allow that.
> >
> > I've seen this a couple of times myself while playing with some
> > progs, but not sure what's the right way to 'fix' it.
> >
> Any thoughts about the patch below? Another way to "fix" it

I'll give it a more thorough look a bit later, but see my comments below.

> would be to mark context accesses 'volatile' in bpf progs, but that sounds
> a bit gross.
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 43b45d6db36d..34a14c950e60 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -746,6 +746,20 @@ bpf_ctx_narrow_access_ok(u32 off, u32 size, u32 size_default)
> return size <= size_default && (size & (size - 1)) == 0;
> }
>
> +static inline bool __bpf_ctx_wide_store_ok(u32 off, u32 size)

It seems like bpf_ctx_wide_store_ok and __bpf_ctx_wide_store_ok are
used only inside net/core/filter.c, why declaring them in header file?

> +{
> + /* u64 access is aligned and fits into the field size */
> + return off % sizeof(__u64) == 0 && off + sizeof(__u64) <= size;
> +}
> +
> +#define bpf_ctx_wide_store_ok(off, size, type, field) \
> + (size == sizeof(__u64) && \
> + off >= offsetof(type, field) && \
> + off < offsetofend(type, field) ? \
> + __bpf_ctx_wide_store_ok(off - offsetof(type, field), \
> + FIELD_SIZEOF(type, field)) : 0)

Why do you need ternary operator instead of just a chain of &&s?

It also seems like you can avoid macro and use plain function if
instead of providing (type, field) you provide values of offsetof and
offsetofend (offsetofend - offsetof should equal FIELD_SIZEOF(type,
field), shouldn't it?).

> +
> +

> #define bpf_classic_proglen(fprog) (fprog->len * sizeof(fprog->filter[0]))
>
> static inline void bpf_prog_lock_ro(struct bpf_prog *fp)
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 2014d76e0d2a..2d3787a439ae 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6849,6 +6849,16 @@ static bool sock_addr_is_valid_access(int off, int size,
> if (!bpf_ctx_narrow_access_ok(off, size, size_default))
> return false;
> } else {
> + if (bpf_ctx_wide_store_ok(off, size,
> + struct bpf_sock_addr,
> + user_ip6))
> + return true;
> +
> + if (bpf_ctx_wide_store_ok(off, size,
> + struct bpf_sock_addr,
> + msg_src_ip6))
> + return true;
> +
> if (size != size_default)
> return false;
> }
> @@ -7689,9 +7699,6 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
> /* SOCK_ADDR_STORE_NESTED_FIELD_OFF() has semantic similar to
> * SOCK_ADDR_LOAD_NESTED_FIELD_SIZE_OFF() but for store operation.
> *
> - * It doesn't support SIZE argument though since narrow stores are not
> - * supported for now.
> - *
> * In addition it uses Temporary Field TF (member of struct S) as the 3rd
> * "register" since two registers available in convert_ctx_access are not
> * enough: we can't override neither SRC, since it contains value to store, nor
> @@ -7699,7 +7706,7 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
> * instructions. But we need a temporary place to save pointer to nested
> * structure whose field we want to store to.
> */
> -#define SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, OFF, TF) \
> +#define SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, SIZE, OFF, TF) \
> do { \
> int tmp_reg = BPF_REG_9; \
> if (si->src_reg == tmp_reg || si->dst_reg == tmp_reg) \
> @@ -7710,8 +7717,7 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
> offsetof(S, TF)); \
> *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(S, F), tmp_reg, \
> si->dst_reg, offsetof(S, F)); \
> - *insn++ = BPF_STX_MEM( \
> - BPF_FIELD_SIZEOF(NS, NF), tmp_reg, si->src_reg, \
> + *insn++ = BPF_STX_MEM(SIZE, tmp_reg, si->src_reg, \
> bpf_target_off(NS, NF, FIELD_SIZEOF(NS, NF), \
> target_size) \
> + OFF); \
> @@ -7723,8 +7729,8 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
> TF) \
> do { \
> if (type == BPF_WRITE) { \
> - SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, OFF, \
> - TF); \
> + SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, SIZE, \
> + OFF, TF); \
> } else { \
> SOCK_ADDR_LOAD_NESTED_FIELD_SIZE_OFF( \
> S, NS, F, NF, SIZE, OFF); \

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Previous message: Saravana Kannan: "[PATCH v2 2/3] of/platform: Add functional dependency link from DT bindings"
In reply to: Stanislav Fomichev: "Re: [bpf/tools] cd17d77705: kernel_selftests.bpf.test_sock_addr.sh.fail"
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