linux-stable.git/kernel/bpf/verifier.c, branch v5.9.8

bpf: Permit map_ptr arithmetic with opcode add and offset 0

2020-11-05T10:51:20+00:00

[ Upstream commit 7c6967326267bd5c0dded0a99541357d70dd11ac ]

Commit 41c48f3a98231 ("bpf: Support access
to bpf map fields") added support to access map fields
with CORE support. For example,

            struct bpf_map {
                    __u32 max_entries;
            } __attribute__((preserve_access_index));

            struct bpf_array {
                    struct bpf_map map;
                    __u32 elem_size;
            } __attribute__((preserve_access_index));

            struct {
                    __uint(type, BPF_MAP_TYPE_ARRAY);
                    __uint(max_entries, 4);
                    __type(key, __u32);
                    __type(value, __u32);
            } m_array SEC(".maps");

            SEC("cgroup_skb/egress")
            int cg_skb(void *ctx)
            {
                    struct bpf_array *array = (struct bpf_array *)&m_array;

                    /* .. array->map.max_entries .. */
            }

In kernel, bpf_htab has similar structure,

	    struct bpf_htab {
		    struct bpf_map map;
                    ...
            }

In the above cg_skb(), to access array->map.max_entries, with CORE, the clang will
generate two builtin's.
            base = &m_array;
            /* access array.map */
            map_addr = __builtin_preserve_struct_access_info(base, 0, 0);
            /* access array.map.max_entries */
            max_entries_addr = __builtin_preserve_struct_access_info(map_addr, 0, 0);
	    max_entries = *max_entries_addr;

In the current llvm, if two builtin's are in the same function or
in the same function after inlining, the compiler is smart enough to chain
them together and generates like below:
            base = &m_array;
            max_entries = *(base + reloc_offset); /* reloc_offset = 0 in this case */
and we are fine.

But if we force no inlining for one of functions in test_map_ptr() selftest, e.g.,
check_default(), the above two __builtin_preserve_* will be in two different
functions. In this case, we will have code like:
   func check_hash():
            reloc_offset_map = 0;
            base = &m_array;
            map_base = base + reloc_offset_map;
            check_default(map_base, ...)
   func check_default(map_base, ...):
            max_entries = *(map_base + reloc_offset_max_entries);

In kernel, map_ptr (CONST_PTR_TO_MAP) does not allow any arithmetic.
The above "map_base = base + reloc_offset_map" will trigger a verifier failure.
  ; VERIFY(check_default(&hash->map, map));
  0: (18) r7 = 0xffffb4fe8018a004
  2: (b4) w1 = 110
  3: (63) *(u32 *)(r7 +0) = r1
   R1_w=invP110 R7_w=map_value(id=0,off=4,ks=4,vs=8,imm=0) R10=fp0
  ; VERIFY_TYPE(BPF_MAP_TYPE_HASH, check_hash);
  4: (18) r1 = 0xffffb4fe8018a000
  6: (b4) w2 = 1
  7: (63) *(u32 *)(r1 +0) = r2
   R1_w=map_value(id=0,off=0,ks=4,vs=8,imm=0) R2_w=invP1 R7_w=map_value(id=0,off=4,ks=4,vs=8,imm=0) R10=fp0
  8: (b7) r2 = 0
  9: (18) r8 = 0xffff90bcb500c000
  11: (18) r1 = 0xffff90bcb500c000
  13: (0f) r1 += r2
  R1 pointer arithmetic on map_ptr prohibited

To fix the issue, let us permit map_ptr + 0 arithmetic which will
result in exactly the same map_ptr.

Signed-off-by: Yonghong Song 
Signed-off-by: Alexei Starovoitov 
Acked-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20200908175702.2463625-1-yhs@fb.com
Signed-off-by: Sasha Levin

bpf: Limit caller's stack depth 256 for subprogs with tailcalls

2020-10-29T09:12:15+00:00

[ Upstream commit 7f6e4312e15a5c370e84eaa685879b6bdcc717e4 ]

Protect against potential stack overflow that might happen when bpf2bpf
calls get combined with tailcalls. Limit the caller's stack depth for
such case down to 256 so that the worst case scenario would result in 8k
stack size (32 which is tailcall limit * 256 = 8k).

Suggested-by: Alexei Starovoitov 
Signed-off-by: Maciej Fijalkowski 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Enforce id generation for all may-be-null register type

2020-10-29T09:11:59+00:00

[ Upstream commit 93c230e3f5bd6e1d2b2759d582fdfe9c2731473b ]

The commit af7ec1383361 ("bpf: Add bpf_skc_to_tcp6_sock() helper")
introduces RET_PTR_TO_BTF_ID_OR_NULL and
the commit eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
introduces RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL.
Note that for RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, the reg0->type
could become PTR_TO_MEM_OR_NULL which is not covered by
BPF_PROBE_MEM.

The BPF_REG_0 will then hold a _OR_NULL pointer type. This _OR_NULL
pointer type requires the bpf program to explicitly do a NULL check first.
After NULL check, the verifier will mark all registers having
the same reg->id as safe to use.  However, the reg->id
is not set for those new _OR_NULL return types.  One of the ways
that may be wrong is, checking NULL for one btf_id typed pointer will
end up validating all other btf_id typed pointers because
all of them have id == 0.  The later tests will exercise
this path.

To fix it and also avoid similar issue in the future, this patch
moves the id generation logic out of each individual RET type
test in check_helper_call().  Instead, it does one
reg_type_may_be_null() test and then do the id generation
if needed.

This patch also adds a WARN_ON_ONCE in mark_ptr_or_null_reg()
to catch future breakage.

The _OR_NULL pointer usage in the bpf_iter_reg.ctx_arg_info is
fine because it just happens that the existing id generation after
check_ctx_access() has covered it.  It is also using the
reg_type_may_be_null() to decide if id generation is needed or not.

Fixes: af7ec1383361 ("bpf: Add bpf_skc_to_tcp6_sock() helper")
Fixes: eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov 
Link: https://lore.kernel.org/bpf/20201019194212.1050855-1-kafai@fb.com
Signed-off-by: Sasha Levin

bpf: disallow attaching modify_return tracing functions to other BPF programs

2020-10-29T09:11:30+00:00

[ Upstream commit 1af9270e908cd50a4f5d815c9b6f794c7d57ed07 ]

From the checks and commit messages for modify_return, it seems it was
never the intention that it should be possible to attach a tracing program
with expected_attach_type == BPF_MODIFY_RETURN to another BPF program.
However, check_attach_modify_return() will only look at the function name,
so if the target function starts with "security_", the attach will be
allowed even for bpf2bpf attachment.

Fix this oversight by also blocking the modification if a target program is
supplied.

Fixes: 18644cec714a ("bpf: Fix use-after-free in fmod_ret check")
Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Acked-by: Andrii Nakryiko 
Signed-off-by: Toke Høiland-Jørgensen 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix scalar32_min_max_or bounds tracking

2020-10-08T09:02:53+00:00

Simon reported an issue with the current scalar32_min_max_or() implementation.
That is, compared to the other 32 bit subreg tracking functions, the code in
scalar32_min_max_or() stands out that it's using the 64 bit registers instead
of 32 bit ones. This leads to bounds tracking issues, for example:

  [...]
  8: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm
  8: (79) r1 = *(u64 *)(r0 +0)
   R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm
  9: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm
  9: (b7) r0 = 1
  10: R0_w=inv1 R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm
  10: (18) r2 = 0x600000002
  12: R0_w=inv1 R1_w=inv(id=0) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  12: (ad) if r1 < r2 goto pc+1
   R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  13: R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  13: (95) exit
  14: R0_w=inv1 R1_w=inv(id=0,umax_value=25769803777,var_off=(0x0; 0x7ffffffff)) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  14: (25) if r1 > 0x0 goto pc+1
   R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  15: R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  15: (95) exit
  16: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=25769803777,var_off=(0x0; 0x77fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  16: (47) r1 |= 0
  17: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=32212254719,var_off=(0x1; 0x700000000),s32_max_value=1,u32_max_value=1) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  [...]

The bound tests on the map value force the upper unsigned bound to be 25769803777
in 64 bit (0b11000000000000000000000000000000001) and then lower one to be 1. By
using OR they are truncated and thus result in the range [1,1] for the 32 bit reg
tracker. This is incorrect given the only thing we know is that the value must be
positive and thus 2147483647 (0b1111111111111111111111111111111) at max for the
subregs. Fix it by using the {u,s}32_{min,max}_value vars instead. This also makes
sense, for example, for the case where we update dst_reg->s32_{min,max}_value in
the else branch we need to use the newly computed dst_reg->u32_{min,max}_value as
we know that these are positive. Previously, in the else branch the 64 bit values
of umin_value=1 and umax_value=32212254719 were used and latter got truncated to
be 1 as upper bound there. After the fix the subreg range is now correct:

  [...]
  8: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm
  8: (79) r1 = *(u64 *)(r0 +0)
   R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm
  9: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm
  9: (b7) r0 = 1
  10: R0_w=inv1 R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm
  10: (18) r2 = 0x600000002
  12: R0_w=inv1 R1_w=inv(id=0) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  12: (ad) if r1 < r2 goto pc+1
   R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  13: R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  13: (95) exit
  14: R0_w=inv1 R1_w=inv(id=0,umax_value=25769803777,var_off=(0x0; 0x7ffffffff)) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  14: (25) if r1 > 0x0 goto pc+1
   R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  15: R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  15: (95) exit
  16: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=25769803777,var_off=(0x0; 0x77fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  16: (47) r1 |= 0
  17: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=32212254719,var_off=(0x0; 0x77fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm
  [...]

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Reported-by: Simon Scannell 
Signed-off-by: Daniel Borkmann 
Reviewed-by: John Fastabend 
Acked-by: Alexei Starovoitov

treewide: Use fallthrough pseudo-keyword

2020-08-23T22:36:59+00:00

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva

bpf: Delete repeated words in comments

2020-08-07T16:57:24+00:00

Drop repeated words in kernel/bpf/: {has, the}

Signed-off-by: Randy Dunlap 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20200807033141.10437-1-rdunlap@infradead.org

bpf: Add missing newline characters in verifier error messages

2020-07-30T22:43:49+00:00

Newline characters are added in two verifier error messages,
refactored in Commit afbf21dce668 ("bpf: Support readonly/readwrite
buffers in verifier"). This way, they do not mix with
messages afterwards.

Signed-off-by: Yonghong Song 
Signed-off-by: Daniel Borkmann 
Acked-by: Song Liu 
Link: https://lore.kernel.org/bpf/20200728221801.1090349-1-yhs@fb.com

bpf: Fix swapped arguments in calls to check_buffer_access

2020-07-28T10:40:10+00:00

There are a couple of arguments of the boolean flag zero_size_allowed and
the char pointer buf_info when calling to function check_buffer_access that
are swapped by mistake. Fix these by swapping them to correct the argument
ordering.

Fixes: afbf21dce668 ("bpf: Support readonly/readwrite buffers in verifier")
Addresses-Coverity: ("Array compared to 0")
Signed-off-by: Colin Ian King 
Signed-off-by: Daniel Borkmann 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20200727175411.155179-1-colin.king@canonical.com

bpf: Fail PERF_EVENT_IOC_SET_BPF when bpf_get_[stack|stackid] cannot work

2020-07-26T03:16:34+00:00

bpf_get_[stack|stackid] on perf_events with precise_ip uses callchain
attached to perf_sample_data. If this callchain is not presented, do not
allow attaching BPF program that calls bpf_get_[stack|stackid] to this
event.

In the error case, -EPROTO is returned so that libbpf can identify this
error and print proper hint message.

Signed-off-by: Song Liu 
Signed-off-by: Alexei Starovoitov 
Link: https://lore.kernel.org/bpf/20200723180648.1429892-3-songliubraving@fb.com