linux-stable.git/kernel/bpf/verifier.c, branch v4.11.2

bpf: don't let ldimm64 leak map addresses on unprivileged

2017-05-14T12:06:02+00:00

[ Upstream commit 0d0e57697f162da4aa218b5feafe614fb666db07 ]

The patch fixes two things at once:

1) It checks the env->allow_ptr_leaks and only prints the map address to
   the log if we have the privileges to do so, otherwise it just dumps 0
   as we would when kptr_restrict is enabled on %pK. Given the latter is
   off by default and not every distro sets it, I don't want to rely on
   this, hence the 0 by default for unprivileged.

2) Printing of ldimm64 in the verifier log is currently broken in that
   we don't print the full immediate, but only the 32 bit part of the
   first insn part for ldimm64. Thus, fix this up as well; it's okay to
   access, since we verified all ldimm64 earlier already (including just
   constants) through replace_map_fd_with_map_ptr().

Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs")
Fixes: cbd357008604 ("bpf: verifier (add ability to receive verification log)")
Reported-by: Jann Horn 
Signed-off-by: Daniel Borkmann 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

bpf: enhance verifier to understand stack pointer arithmetic

2017-05-14T12:06:01+00:00

[ Upstream commit 332270fdc8b6fba07d059a9ad44df9e1a2ad4529 ]

llvm 4.0 and above generates the code like below:
....
440: (b7) r1 = 15
441: (05) goto pc+73
515: (79) r6 = *(u64 *)(r10 -152)
516: (bf) r7 = r10
517: (07) r7 += -112
518: (bf) r2 = r7
519: (0f) r2 += r1
520: (71) r1 = *(u8 *)(r8 +0)
521: (73) *(u8 *)(r2 +45) = r1
....
and the verifier complains "R2 invalid mem access 'inv'" for insn #521.
This is because verifier marks register r2 as unknown value after #519
where r2 is a stack pointer and r1 holds a constant value.

Teach verifier to recognize "stack_ptr + imm" and
"stack_ptr + reg with const val" as valid stack_ptr with new offset.

Signed-off-by: Yonghong Song 
Acked-by: Martin KaFai Lau 
Acked-by: Daniel Borkmann 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

bpf, verifier: fix rejection of unaligned access checks for map_value_adj

2017-04-01T19:36:37+00:00

Currently, the verifier doesn't reject unaligned access for map_value_adj
register types. Commit 484611357c19 ("bpf: allow access into map value
arrays") added logic to check_ptr_alignment() extending it from PTR_TO_PACKET
to also PTR_TO_MAP_VALUE_ADJ, but for PTR_TO_MAP_VALUE_ADJ no enforcement
is in place, because reg->id for PTR_TO_MAP_VALUE_ADJ reg types is never
non-zero, meaning, we can cause BPF_H/_W/_DW-based unaligned access for
architectures not supporting efficient unaligned access, and thus worst
case could raise exceptions on some archs that are unable to correct the
unaligned access or perform a different memory access to the actual
requested one and such.

i) Unaligned load with !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
   on r0 (map_value_adj):

   0: (bf) r2 = r10
   1: (07) r2 += -8
   2: (7a) *(u64 *)(r2 +0) = 0
   3: (18) r1 = 0x42533a00
   5: (85) call bpf_map_lookup_elem#1
   6: (15) if r0 == 0x0 goto pc+11
    R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp
   7: (61) r1 = *(u32 *)(r0 +0)
   8: (35) if r1 >= 0xb goto pc+9
    R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R1=inv,min_value=0,max_value=10 R10=fp
   9: (07) r0 += 3
  10: (79) r7 = *(u64 *)(r0 +0)
    R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R1=inv,min_value=0,max_value=10 R10=fp
  11: (79) r7 = *(u64 *)(r0 +2)
    R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R1=inv,min_value=0,max_value=10 R7=inv R10=fp
  [...]

ii) Unaligned store with !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
    on r0 (map_value_adj):

   0: (bf) r2 = r10
   1: (07) r2 += -8
   2: (7a) *(u64 *)(r2 +0) = 0
   3: (18) r1 = 0x4df16a00
   5: (85) call bpf_map_lookup_elem#1
   6: (15) if r0 == 0x0 goto pc+19
    R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp
   7: (07) r0 += 3
   8: (7a) *(u64 *)(r0 +0) = 42
    R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R10=fp
   9: (7a) *(u64 *)(r0 +2) = 43
    R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R10=fp
  10: (7a) *(u64 *)(r0 -2) = 44
    R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R10=fp
  [...]

For the PTR_TO_PACKET type, reg->id is initially zero when skb->data
was fetched, it later receives a reg->id from env->id_gen generator
once another register with UNKNOWN_VALUE type was added to it via
check_packet_ptr_add(). The purpose of this reg->id is twofold: i) it
is used in find_good_pkt_pointers() for setting the allowed access
range for regs with PTR_TO_PACKET of same id once verifier matched
on data/data_end tests, and ii) for check_ptr_alignment() to determine
that when not having efficient unaligned access and register with
UNKNOWN_VALUE was added to PTR_TO_PACKET, that we're only allowed
to access the content bytewise due to unknown unalignment. reg->id
was never intended for PTR_TO_MAP_VALUE{,_ADJ} types and thus is
always zero, the only marking is in PTR_TO_MAP_VALUE_OR_NULL that
was added after 484611357c19 via 57a09bf0a416 ("bpf: Detect identical
PTR_TO_MAP_VALUE_OR_NULL registers"). Above tests will fail for
non-root environment due to prohibited pointer arithmetic.

The fix splits register-type specific checks into their own helper
instead of keeping them combined, so we don't run into a similar
issue in future once we extend check_ptr_alignment() further and
forget to add reg->type checks for some of the checks.

Fixes: 484611357c19 ("bpf: allow access into map value arrays")
Signed-off-by: Daniel Borkmann 
Reviewed-by: Josef Bacik 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf, verifier: fix alu ops against map_value{, _adj} register types

2017-04-01T19:36:37+00:00

While looking into map_value_adj, I noticed that alu operations
directly on the map_value() resp. map_value_adj() register (any
alu operation on a map_value() register will turn it into a
map_value_adj() typed register) are not sufficiently protected
against some of the operations. Two non-exhaustive examples are
provided that the verifier needs to reject:

 i) BPF_AND on r0 (map_value_adj):

  0: (bf) r2 = r10
  1: (07) r2 += -8
  2: (7a) *(u64 *)(r2 +0) = 0
  3: (18) r1 = 0xbf842a00
  5: (85) call bpf_map_lookup_elem#1
  6: (15) if r0 == 0x0 goto pc+2
   R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp
  7: (57) r0 &= 8
  8: (7a) *(u64 *)(r0 +0) = 22
   R0=map_value_adj(ks=8,vs=48,id=0),min_value=0,max_value=8 R10=fp
  9: (95) exit

  from 6 to 9: R0=inv,min_value=0,max_value=0 R10=fp
  9: (95) exit
  processed 10 insns

ii) BPF_ADD in 32 bit mode on r0 (map_value_adj):

  0: (bf) r2 = r10
  1: (07) r2 += -8
  2: (7a) *(u64 *)(r2 +0) = 0
  3: (18) r1 = 0xc24eee00
  5: (85) call bpf_map_lookup_elem#1
  6: (15) if r0 == 0x0 goto pc+2
   R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp
  7: (04) (u32) r0 += (u32) 0
  8: (7a) *(u64 *)(r0 +0) = 22
   R0=map_value_adj(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp
  9: (95) exit

  from 6 to 9: R0=inv,min_value=0,max_value=0 R10=fp
  9: (95) exit
  processed 10 insns

Issue is, while min_value / max_value boundaries for the access
are adjusted appropriately, we change the pointer value in a way
that cannot be sufficiently tracked anymore from its origin.
Operations like BPF_{AND,OR,DIV,MUL,etc} on a destination register
that is PTR_TO_MAP_VALUE{,_ADJ} was probably unintended, in fact,
all the test cases coming with 484611357c19 ("bpf: allow access
into map value arrays") perform BPF_ADD only on the destination
register that is PTR_TO_MAP_VALUE_ADJ.

Only for UNKNOWN_VALUE register types such operations make sense,
f.e. with unknown memory content fetched initially from a constant
offset from the map value memory into a register. That register is
then later tested against lower / upper bounds, so that the verifier
can then do the tracking of min_value / max_value, and properly
check once that UNKNOWN_VALUE register is added to the destination
register with type PTR_TO_MAP_VALUE{,_ADJ}. This is also what the
original use-case is solving. Note, tracking on what is being
added is done through adjust_reg_min_max_vals() and later access
to the map value enforced with these boundaries and the given offset
from the insn through check_map_access_adj().

Tests will fail for non-root environment due to prohibited pointer
arithmetic, in particular in check_alu_op(), we bail out on the
is_pointer_value() check on the dst_reg (which is false in root
case as we allow for pointer arithmetic via env->allow_ptr_leaks).

Similarly to PTR_TO_PACKET, one way to fix it is to restrict the
allowed operations on PTR_TO_MAP_VALUE{,_ADJ} registers to 64 bit
mode BPF_ADD. The test_verifier suite runs fine after the patch
and it also rejects mentioned test cases.

Fixes: 484611357c19 ("bpf: allow access into map value arrays")
Signed-off-by: Daniel Borkmann 
Reviewed-by: Josef Bacik 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: improve verifier packet range checks

2017-03-25T03:51:28+00:00

llvm can optimize the 'if (ptr > data_end)' checks to be in the order
slightly different than the original C code which will confuse verifier.
Like:
if (ptr + 16 > data_end)
  return TC_ACT_SHOT;
// may be followed by
if (ptr + 14 > data_end)
  return TC_ACT_SHOT;
while llvm can see that 'ptr' is valid for all 16 bytes,
the verifier could not.
Fix verifier logic to account for such case and add a test.

Reported-by: Huapeng Zhou 
Fixes: 969bf05eb3ce ("bpf: direct packet access")
Signed-off-by: Alexei Starovoitov 
Acked-by: Daniel Borkmann 
Acked-by: Martin KaFai Lau 
Signed-off-by: David S. Miller

bpf: update the comment about the length of analysis

2017-03-01T22:56:50+00:00

Commit 07016151a446 ("bpf, verifier: further improve search
pruning") increased the limit of processed instructions from
32k to 64k, but the comment still mentioned the 32k limit.
This commit updates the comment to reflect the change.

Cc: Alexei Starovoitov 
Cc: Daniel Borkmann 
Signed-off-by: Gary Lin 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: fix spelling mistake: "proccessed" -> "processed"

2017-02-23T15:46:08+00:00

trivial fix to spelling mistake in verbose log message

Signed-off-by: Colin Ian King 
Signed-off-by: David S. Miller

bpf: reduce compiler warnings by adding fallthrough comments

2017-02-14T19:32:12+00:00

Fixes the following warnings:

kernel/bpf/verifier.c: In function ‘may_access_direct_pkt_data’:
kernel/bpf/verifier.c:702:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (t == BPF_WRITE)
      ^
kernel/bpf/verifier.c:704:2: note: here
  case BPF_PROG_TYPE_SCHED_CLS:
  ^~~~
kernel/bpf/verifier.c: In function ‘reg_set_min_max_inv’:
kernel/bpf/verifier.c:2057:23: warning: this statement may fall through [-Wimplicit-fallthrough=]
   true_reg->min_value = 0;
   ~~~~~~~~~~~~~~~~~~~~^~~
kernel/bpf/verifier.c:2058:2: note: here
  case BPF_JSGT:
  ^~~~
kernel/bpf/verifier.c:2068:23: warning: this statement may fall through [-Wimplicit-fallthrough=]
   true_reg->min_value = 0;
   ~~~~~~~~~~~~~~~~~~~~^~~
kernel/bpf/verifier.c:2069:2: note: here
  case BPF_JSGE:
  ^~~~
kernel/bpf/verifier.c: In function ‘reg_set_min_max’:
kernel/bpf/verifier.c:2009:24: warning: this statement may fall through [-Wimplicit-fallthrough=]
   false_reg->min_value = 0;
   ~~~~~~~~~~~~~~~~~~~~~^~~
kernel/bpf/verifier.c:2010:2: note: here
  case BPF_JSGT:
  ^~~~
kernel/bpf/verifier.c:2019:24: warning: this statement may fall through [-Wimplicit-fallthrough=]
   false_reg->min_value = 0;
   ~~~~~~~~~~~~~~~~~~~~~^~~
kernel/bpf/verifier.c:2020:2: note: here
  case BPF_JSGE:
  ^~~~

Reported-by: David Binderman 
Signed-off-by: Alexander Alemayhu 
Acked-by: Daniel Borkmann 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: enable verifier to add 0 to packet ptr

2017-02-07T03:50:04+00:00

The patch fixes the case when adding a zero value to the packet
pointer.  The zero value could come from src_reg equals type
BPF_K or CONST_IMM.  The patch fixes both, otherwise the verifer
reports the following error:
  [...]
    R0=imm0,min_value=0,max_value=0
    R1=pkt(id=0,off=0,r=4)
    R2=pkt_end R3=fp-12
    R4=imm4,min_value=4,max_value=4
    R5=pkt(id=0,off=4,r=4)
  269: (bf) r2 = r0     // r2 becomes imm0
  270: (77) r2 >>= 3
  271: (bf) r4 = r1     // r4 becomes pkt ptr
  272: (0f) r4 += r2    // r4 += 0
  addition of negative constant to packet pointer is not allowed

Signed-off-by: William Tu 
Signed-off-by: Mihai Budiu 
Cc: Daniel Borkmann 
Cc: Alexei Starovoitov 
Acked-by: Daniel Borkmann 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: enable verifier to better track const alu ops

2017-01-24T19:46:06+00:00

William reported couple of issues in relation to direct packet
access. Typical scheme is to check for data + [off] <= data_end,
where [off] can be either immediate or coming from a tracked
register that contains an immediate, depending on the branch, we
can then access the data. However, in case of calculating [off]
for either the mentioned test itself or for access after the test
in a more "complex" way, then the verifier will stop tracking the
CONST_IMM marked register and will mark it as UNKNOWN_VALUE one.

Adding that UNKNOWN_VALUE typed register to a pkt() marked
register, the verifier then bails out in check_packet_ptr_add()
as it finds the registers imm value below 48. In the first below
example, that is due to evaluate_reg_imm_alu() not handling right
shifts and thus marking the register as UNKNOWN_VALUE via helper
__mark_reg_unknown_value() that resets imm to 0.

In the second case the same happens at the time when r4 is set
to r4 &= r5, where it transitions to UNKNOWN_VALUE from
evaluate_reg_imm_alu(). Later on r4 we shift right by 3 inside
evaluate_reg_alu(), where the register's imm turns into 3. That
is, for registers with type UNKNOWN_VALUE, imm of 0 means that
we don't know what value the register has, and for imm > 0 it
means that the value has [imm] upper zero bits. F.e. when shifting
an UNKNOWN_VALUE register by 3 to the right, no matter what value
it had, we know that the 3 upper most bits must be zero now.
This is to make sure that ALU operations with unknown registers
don't overflow. Meaning, once we know that we have more than 48
upper zero bits, or, in other words cannot go beyond 0xffff offset
with ALU ops, such an addition will track the target register
as a new pkt() register with a new id, but 0 offset and 0 range,
so for that a new data/data_end test will be required. Is the source
register a CONST_IMM one that is to be added to the pkt() register,
or the source instruction is an add instruction with immediate
value, then it will get added if it stays within max 0xffff bounds.
>From there, pkt() type, can be accessed should reg->off + imm be
within the access range of pkt().

  [...]
  from 28 to 30: R0=imm1,min_value=1,max_value=1
    R1=pkt(id=0,off=0,r=22) R2=pkt_end
    R3=imm144,min_value=144,max_value=144
    R4=imm0,min_value=0,max_value=0
    R5=inv48,min_value=2054,max_value=2054 R10=fp
  30: (bf) r5 = r3
  31: (07) r5 += 23
  32: (77) r5 >>= 3
  33: (bf) r6 = r1
  34: (0f) r6 += r5
  cannot add integer value with 0 upper zero bits to ptr_to_packet

  [...]
  from 52 to 80: R0=imm1,min_value=1,max_value=1
    R1=pkt(id=0,off=0,r=34) R2=pkt_end R3=inv
    R4=imm272 R5=inv56,min_value=17,max_value=17
    R6=pkt(id=0,off=26,r=34) R10=fp
  80: (07) r4 += 71
  81: (18) r5 = 0xfffffff8
  83: (5f) r4 &= r5
  84: (77) r4 >>= 3
  85: (0f) r1 += r4
  cannot add integer value with 3 upper zero bits to ptr_to_packet

Thus to get above use-cases working, evaluate_reg_imm_alu() has
been extended for further ALU ops. This is fine, because we only
operate strictly within realm of CONST_IMM types, so here we don't
care about overflows as they will happen in the simulated but also
real execution and interaction with pkt() in check_packet_ptr_add()
will check actual imm value once added to pkt(), but it's irrelevant
before.

With regards to 06c1c049721a ("bpf: allow helpers access to variable
memory") that works on UNKNOWN_VALUE registers, the verifier becomes
now a bit smarter as it can better resolve ALU ops, so we need to
adapt two test cases there, as min/max bound tracking only becomes
necessary when registers were spilled to stack. So while mask was
set before to track upper bound for UNKNOWN_VALUE case, it's now
resolved directly as CONST_IMM, and such contructs are only necessary
when f.e. registers are spilled.

For commit 6b17387307ba ("bpf: recognize 64bit immediate loads as
consts") that initially enabled dw load tracking only for nfp jit/
analyzer, I did couple of tests on large, complex programs and we
don't increase complexity badly (my tests were in ~3% range on avg).
I've added a couple of tests similar to affected code above, and
it works fine with verifier now.

Reported-by: William Tu 
Signed-off-by: Daniel Borkmann 
Cc: Gianluca Borello 
Cc: William Tu 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller