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* [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling
@ 2020-03-30 16:03 Daniel Borkmann
  2020-03-30 16:03 ` [PATCH bpf-next 1/3] bpf: Undo incorrect " Daniel Borkmann
                   ` (3 more replies)
  0 siblings, 4 replies; 5+ messages in thread
From: Daniel Borkmann @ 2020-03-30 16:03 UTC (permalink / raw)
  To: alexei.starovoitov
  Cc: jannh, yhs, john.fastabend, bpf, netdev, Daniel Borkmann

Fix for the verifier's __reg_bound_offset32() handling, please see individual
patches for details.

Thanks!

Daniel Borkmann (1):
  bpf: Undo incorrect __reg_bound_offset32 handling

Jann Horn (2):
  bpf: Fix tnum constraints for 32-bit comparisons
  bpf: Simplify reg_set_min_max_inv handling

 kernel/bpf/verifier.c | 227 +++++++++++++++++-------------------------
 1 file changed, 90 insertions(+), 137 deletions(-)

-- 
2.20.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* [PATCH bpf-next 1/3] bpf: Undo incorrect __reg_bound_offset32 handling
  2020-03-30 16:03 [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Daniel Borkmann
@ 2020-03-30 16:03 ` Daniel Borkmann
  2020-03-30 16:03 ` [PATCH bpf-next 2/3] bpf: Fix tnum constraints for 32-bit comparisons Daniel Borkmann
                   ` (2 subsequent siblings)
  3 siblings, 0 replies; 5+ messages in thread
From: Daniel Borkmann @ 2020-03-30 16:03 UTC (permalink / raw)
  To: alexei.starovoitov
  Cc: jannh, yhs, john.fastabend, bpf, netdev, Daniel Borkmann,
	Anatoly Trosinenko

Anatoly has been fuzzing with kBdysch harness and reported a hang in
one of the outcomes:

  0: (b7) r0 = 808464432
  1: (7f) r0 >>= r0
  2: (14) w0 -= 808464432
  3: (07) r0 += 808464432
  4: (b7) r1 = 808464432
  5: (de) if w1 s<= w0 goto pc+0
   R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x30303020;0x10000001f)) R1_w=invP808464432 R10=fp0
  6: (07) r0 += -2144337872
  7: (14) w0 -= -1607454672
  8: (25) if r0 > 0x30303030 goto pc+0
   R0_w=invP(id=0,umin_value=271581184,umax_value=271581311,var_off=(0x10300000;0x7f)) R1_w=invP808464432 R10=fp0
  9: (76) if w0 s>= 0x303030 goto pc+2
  12: (95) exit

  from 8 to 9: safe

  from 5 to 6: R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x30303020;0x10000001f)) R1_w=invP808464432 R10=fp0
  6: (07) r0 += -2144337872
  7: (14) w0 -= -1607454672
  8: (25) if r0 > 0x30303030 goto pc+0
   R0_w=invP(id=0,umin_value=271581184,umax_value=271581311,var_off=(0x10300000;0x7f)) R1_w=invP808464432 R10=fp0
  9: safe

  from 8 to 9: safe
  verification time 589 usec
  stack depth 0
  processed 17 insns (limit 1000000) [...]

The underlying program was xlated as follows:

  # bpftool p d x i 9
   0: (b7) r0 = 808464432
   1: (7f) r0 >>= r0
   2: (14) w0 -= 808464432
   3: (07) r0 += 808464432
   4: (b7) r1 = 808464432
   5: (de) if w1 s<= w0 goto pc+0
   6: (07) r0 += -2144337872
   7: (14) w0 -= -1607454672
   8: (25) if r0 > 0x30303030 goto pc+0
   9: (76) if w0 s>= 0x303030 goto pc+2
  10: (05) goto pc-1
  11: (05) goto pc-1
  12: (95) exit

The verifier rewrote original instructions it recognized as dead code with
'goto pc-1', but reality differs from verifier simulation in that we're
actually able to trigger a hang due to hitting the 'goto pc-1' instructions.

Taking different examples to make the issue more obvious: in this example
we're probing bounds on a completely unknown scalar variable in r1:

  [...]
  5: R0_w=inv1 R1_w=inv(id=0) R10=fp0
  5: (18) r2 = 0x4000000000
  7: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R10=fp0
  7: (18) r3 = 0x2000000000
  9: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R3_w=inv137438953472 R10=fp0
  9: (18) r4 = 0x400
  11: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R10=fp0
  11: (18) r5 = 0x200
  13: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0
  13: (2d) if r1 > r2 goto pc+4
   R0_w=inv1 R1_w=inv(id=0,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0
  14: R0_w=inv1 R1_w=inv(id=0,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0
  14: (ad) if r1 < r3 goto pc+3
   R0_w=inv1 R1_w=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0
  15: R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0
  15: (2e) if w1 > w4 goto pc+2
   R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7f00000000)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0
  16: R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7f00000000)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0
  16: (ae) if w1 < w5 goto pc+1
   R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7f00000000)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0
  [...]

We're first probing lower/upper bounds via jmp64, later we do a similar
check via jmp32 and examine the resulting var_off there. After fall-through
in insn 14, we get the following bounded r1 with 0x7fffffffff unknown marked
bits in the variable section.

Thus, after knowing r1 <= 0x4000000000 and r1 >= 0x2000000000:

  max: 0b100000000000000000000000000000000000000 / 0x4000000000
  var: 0b111111111111111111111111111111111111111 / 0x7fffffffff
  min: 0b010000000000000000000000000000000000000 / 0x2000000000

Now, in insn 15 and 16, we perform a similar probe with lower/upper bounds
in jmp32.

Thus, after knowing r1 <= 0x4000000000 and r1 >= 0x2000000000 and
                    w1 <= 0x400        and w1 >= 0x200:

  max: 0b100000000000000000000000000000000000000 / 0x4000000000
  var: 0b111111100000000000000000000000000000000 / 0x7f00000000
  min: 0b010000000000000000000000000000000000000 / 0x2000000000

The lower/upper bounds haven't changed since they have high bits set in
u64 space and the jmp32 tests can only refine bounds in the low bits.

However, for the var part the expectation would have been 0x7f000007ff
or something less precise up to 0x7fffffffff. A outcome of 0x7f00000000
is not correct since it would contradict the earlier probed bounds
where we know that the result should have been in [0x200,0x400] in u32
space. Therefore, tests with such info will lead to wrong verifier
assumptions later on like falsely predicting conditional jumps to be
always taken, etc.

The issue here is that __reg_bound_offset32()'s implementation from
commit 581738a681b6 ("bpf: Provide better register bounds after jmp32
instructions") makes an incorrect range assumption:

  static void __reg_bound_offset32(struct bpf_reg_state *reg)
  {
        u64 mask = 0xffffFFFF;
        struct tnum range = tnum_range(reg->umin_value & mask,
                                       reg->umax_value & mask);
        struct tnum lo32 = tnum_cast(reg->var_off, 4);
        struct tnum hi32 = tnum_lshift(tnum_rshift(reg->var_off, 32), 32);

        reg->var_off = tnum_or(hi32, tnum_intersect(lo32, range));
  }

In the above walk-through example, __reg_bound_offset32() as-is chose
a range after masking with 0xffffffff of [0x0,0x0] since umin:0x2000000000
and umax:0x4000000000 and therefore the lo32 part was clamped to 0x0 as
well. However, in the umin:0x2000000000 and umax:0x4000000000 range above
we'd end up with an actual possible interval of [0x0,0xffffffff] for u32
space instead.

In case of the original reproducer, the situation looked as follows at
insn 5 for r0:

  [...]
  5: R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x0; 0x1ffffffff)) R1_w=invP808464432 R10=fp0
                               0x30303030           0x13030302f
  5: (de) if w1 s<= w0 goto pc+0
   R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x30303020; 0x10000001f)) R1_w=invP808464432 R10=fp0
                             0x30303030           0x13030302f
  [...]

After the fall-through, we similarly forced the var_off result into
the wrong range [0x30303030,0x3030302f] suggesting later on that fixed
bits must only be of 0x30303020 with 0x10000001f unknowns whereas such
assumption can only be made when both bounds in hi32 range match.

Originally, I was thinking to fix this by moving reg into a temp reg and
use proper coerce_reg_to_size() helper on the temp reg where we can then
based on that define the range tnum for later intersection:

  static void __reg_bound_offset32(struct bpf_reg_state *reg)
  {
        struct bpf_reg_state tmp = *reg;
        struct tnum lo32, hi32, range;

        coerce_reg_to_size(&tmp, 4);
        range = tnum_range(tmp.umin_value, tmp.umax_value);
        lo32 = tnum_cast(reg->var_off, 4);
        hi32 = tnum_lshift(tnum_rshift(reg->var_off, 32), 32);
        reg->var_off = tnum_or(hi32, tnum_intersect(lo32, range));
  }

In the case of the concrete example, this gives us a more conservative unknown
section. Thus, after knowing r1 <= 0x4000000000 and r1 >= 0x2000000000 and
                             w1 <= 0x400        and w1 >= 0x200:

  max: 0b100000000000000000000000000000000000000 / 0x4000000000
  var: 0b111111111111111111111111111111111111111 / 0x7fffffffff
  min: 0b010000000000000000000000000000000000000 / 0x2000000000

However, above new __reg_bound_offset32() has no effect on refining the
knowledge of the register contents. Meaning, if the bounds in hi32 range
mismatch we'll get the identity function given the range reg spans
[0x0,0xffffffff] and we cast var_off into lo32 only to later on binary
or it again with the hi32.

Likewise, if the bounds in hi32 range match, then we mask both bounds
with 0xffffffff, use the resulting umin/umax for the range to later
intersect the lo32 with it. However, _prior_ called __reg_bound_offset()
did already such intersection on the full reg and we therefore would only
repeat the same operation on the lo32 part twice.

Given this has no effect and the original commit had false assumptions,
this patch reverts the code entirely which is also more straight forward
for stable trees: apparently 581738a681b6 got auto-selected by Sasha's
ML system and misclassified as a fix, so it got sucked into v5.4 where
it should never have landed. A revert is low-risk also from a user PoV
since it requires a recent kernel and llc to opt-into -mcpu=v3 BPF CPU
to generate jmp32 instructions. A proper bounds refinement would need a
significantly more complex approach which is currently being worked, but
no stable material [0]. Hence revert is best option for stable. After the
revert, the original reported program gets rejected as follows:

  1: (7f) r0 >>= r0
  2: (14) w0 -= 808464432
  3: (07) r0 += 808464432
  4: (b7) r1 = 808464432
  5: (de) if w1 s<= w0 goto pc+0
   R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x0; 0x1ffffffff)) R1_w=invP808464432 R10=fp0
  6: (07) r0 += -2144337872
  7: (14) w0 -= -1607454672
  8: (25) if r0 > 0x30303030 goto pc+0
   R0_w=invP(id=0,umax_value=808464432,var_off=(0x0; 0x3fffffff)) R1_w=invP808464432 R10=fp0
  9: (76) if w0 s>= 0x303030 goto pc+2
   R0=invP(id=0,umax_value=3158063,var_off=(0x0; 0x3fffff)) R1=invP808464432 R10=fp0
  10: (30) r0 = *(u8 *)skb[808464432]
  BPF_LD_[ABS|IND] uses reserved fields
  processed 11 insns (limit 1000000) [...]

  [0] https://lore.kernel.org/bpf/158507130343.15666.8018068546764556975.stgit@john-Precision-5820-Tower/T/

Fixes: 581738a681b6 ("bpf: Provide better register bounds after jmp32 instructions")
Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 047b2e876399..2a84f73a93a1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1036,17 +1036,6 @@ static void __reg_bound_offset(struct bpf_reg_state *reg)
 						 reg->umax_value));
 }
 
-static void __reg_bound_offset32(struct bpf_reg_state *reg)
-{
-	u64 mask = 0xffffFFFF;
-	struct tnum range = tnum_range(reg->umin_value & mask,
-				       reg->umax_value & mask);
-	struct tnum lo32 = tnum_cast(reg->var_off, 4);
-	struct tnum hi32 = tnum_lshift(tnum_rshift(reg->var_off, 32), 32);
-
-	reg->var_off = tnum_or(hi32, tnum_intersect(lo32, range));
-}
-
 /* Reset the min/max bounds of a register */
 static void __mark_reg_unbounded(struct bpf_reg_state *reg)
 {
@@ -5805,10 +5794,6 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
 	/* We might have learned some bits from the bounds. */
 	__reg_bound_offset(false_reg);
 	__reg_bound_offset(true_reg);
-	if (is_jmp32) {
-		__reg_bound_offset32(false_reg);
-		__reg_bound_offset32(true_reg);
-	}
 	/* Intersecting with the old var_off might have improved our bounds
 	 * slightly.  e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc),
 	 * then new var_off is (0; 0x7f...fc) which improves our umax.
@@ -5918,10 +5903,6 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
 	/* We might have learned some bits from the bounds. */
 	__reg_bound_offset(false_reg);
 	__reg_bound_offset(true_reg);
-	if (is_jmp32) {
-		__reg_bound_offset32(false_reg);
-		__reg_bound_offset32(true_reg);
-	}
 	/* Intersecting with the old var_off might have improved our bounds
 	 * slightly.  e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc),
 	 * then new var_off is (0; 0x7f...fc) which improves our umax.
-- 
2.20.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* [PATCH bpf-next 2/3] bpf: Fix tnum constraints for 32-bit comparisons
  2020-03-30 16:03 [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Daniel Borkmann
  2020-03-30 16:03 ` [PATCH bpf-next 1/3] bpf: Undo incorrect " Daniel Borkmann
@ 2020-03-30 16:03 ` Daniel Borkmann
  2020-03-30 16:03 ` [PATCH bpf-next 3/3] bpf: Simplify reg_set_min_max_inv handling Daniel Borkmann
  2020-03-30 19:01 ` [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Alexei Starovoitov
  3 siblings, 0 replies; 5+ messages in thread
From: Daniel Borkmann @ 2020-03-30 16:03 UTC (permalink / raw)
  To: alexei.starovoitov
  Cc: jannh, yhs, john.fastabend, bpf, netdev, Daniel Borkmann

From: Jann Horn <jannh@google.com>

The BPF verifier tried to track values based on 32-bit comparisons by
(ab)using the tnum state via 581738a681b6 ("bpf: Provide better register
bounds after jmp32 instructions"). The idea is that after a check like
this:

    if ((u32)r0 > 3)
      exit

We can't meaningfully constrain the arithmetic-range-based tracking, but
we can update the tnum state to (value=0,mask=0xffff'ffff'0000'0003).
However, the implementation from 581738a681b6 didn't compute the tnum
constraint based on the fixed operand, but instead derives it from the
arithmetic-range-based tracking. This means that after the following
sequence of operations:

    if (r0 >= 0x1'0000'0001)
      exit
    if ((u32)r0 > 7)
      exit

The verifier assumed that the lower half of r0 is in the range (0, 0)
and apply the tnum constraint (value=0,mask=0xffff'ffff'0000'0000) thus
causing the overall tnum to be (value=0,mask=0x1'0000'0000), which was
incorrect. Provide a fixed implementation.

Fixes: 581738a681b6 ("bpf: Provide better register bounds after jmp32 instructions")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 108 ++++++++++++++++++++++++++++--------------
 1 file changed, 72 insertions(+), 36 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2a84f73a93a1..6fce6f096c16 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5678,6 +5678,70 @@ static bool cmp_val_with_extended_s64(s64 sval, struct bpf_reg_state *reg)
 		reg->smax_value <= 0 && reg->smin_value >= S32_MIN);
 }
 
+/* Constrain the possible values of @reg with unsigned upper bound @bound.
+ * If @is_exclusive, @bound is an exclusive limit, otherwise it is inclusive.
+ * If @is_jmp32, @bound is a 32-bit value that only constrains the low 32 bits
+ * of @reg.
+ */
+static void set_upper_bound(struct bpf_reg_state *reg, u64 bound, bool is_jmp32,
+			    bool is_exclusive)
+{
+	if (is_exclusive) {
+		/* There are no values for `reg` that make `reg<0` true. */
+		if (bound == 0)
+			return;
+		bound--;
+	}
+	if (is_jmp32) {
+		/* Constrain the register's value in the tnum representation.
+		 * For 64-bit comparisons this happens later in
+		 * __reg_bound_offset(), but for 32-bit comparisons, we can be
+		 * more precise than what can be derived from the updated
+		 * numeric bounds.
+		 */
+		struct tnum t = tnum_range(0, bound);
+
+		t.mask |= ~0xffffffffULL; /* upper half is unknown */
+		reg->var_off = tnum_intersect(reg->var_off, t);
+
+		/* Compute the 64-bit bound from the 32-bit bound. */
+		bound += gen_hi_max(reg->var_off);
+	}
+	reg->umax_value = min(reg->umax_value, bound);
+}
+
+/* Constrain the possible values of @reg with unsigned lower bound @bound.
+ * If @is_exclusive, @bound is an exclusive limit, otherwise it is inclusive.
+ * If @is_jmp32, @bound is a 32-bit value that only constrains the low 32 bits
+ * of @reg.
+ */
+static void set_lower_bound(struct bpf_reg_state *reg, u64 bound, bool is_jmp32,
+			    bool is_exclusive)
+{
+	if (is_exclusive) {
+		/* There are no values for `reg` that make `reg>MAX` true. */
+		if (bound == (is_jmp32 ? U32_MAX : U64_MAX))
+			return;
+		bound++;
+	}
+	if (is_jmp32) {
+		/* Constrain the register's value in the tnum representation.
+		 * For 64-bit comparisons this happens later in
+		 * __reg_bound_offset(), but for 32-bit comparisons, we can be
+		 * more precise than what can be derived from the updated
+		 * numeric bounds.
+		 */
+		struct tnum t = tnum_range(bound, U32_MAX);
+
+		t.mask |= ~0xffffffffULL; /* upper half is unknown */
+		reg->var_off = tnum_intersect(reg->var_off, t);
+
+		/* Compute the 64-bit bound from the 32-bit bound. */
+		bound += gen_hi_min(reg->var_off);
+	}
+	reg->umin_value = max(reg->umin_value, bound);
+}
+
 /* Adjusts the register min/max values in the case that the dst_reg is the
  * variable register that we are working on, and src_reg is a constant or we're
  * simply doing a BPF_K check.
@@ -5733,15 +5797,8 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
 	case BPF_JGE:
 	case BPF_JGT:
 	{
-		u64 false_umax = opcode == BPF_JGT ? val    : val - 1;
-		u64 true_umin = opcode == BPF_JGT ? val + 1 : val;
-
-		if (is_jmp32) {
-			false_umax += gen_hi_max(false_reg->var_off);
-			true_umin += gen_hi_min(true_reg->var_off);
-		}
-		false_reg->umax_value = min(false_reg->umax_value, false_umax);
-		true_reg->umin_value = max(true_reg->umin_value, true_umin);
+		set_upper_bound(false_reg, val, is_jmp32, opcode == BPF_JGE);
+		set_lower_bound(true_reg, val, is_jmp32, opcode == BPF_JGT);
 		break;
 	}
 	case BPF_JSGE:
@@ -5762,15 +5819,8 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
 	case BPF_JLE:
 	case BPF_JLT:
 	{
-		u64 false_umin = opcode == BPF_JLT ? val    : val + 1;
-		u64 true_umax = opcode == BPF_JLT ? val - 1 : val;
-
-		if (is_jmp32) {
-			false_umin += gen_hi_min(false_reg->var_off);
-			true_umax += gen_hi_max(true_reg->var_off);
-		}
-		false_reg->umin_value = max(false_reg->umin_value, false_umin);
-		true_reg->umax_value = min(true_reg->umax_value, true_umax);
+		set_lower_bound(false_reg, val, is_jmp32, opcode == BPF_JLE);
+		set_upper_bound(true_reg, val, is_jmp32, opcode == BPF_JLT);
 		break;
 	}
 	case BPF_JSLE:
@@ -5845,15 +5895,8 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
 	case BPF_JGE:
 	case BPF_JGT:
 	{
-		u64 false_umin = opcode == BPF_JGT ? val    : val + 1;
-		u64 true_umax = opcode == BPF_JGT ? val - 1 : val;
-
-		if (is_jmp32) {
-			false_umin += gen_hi_min(false_reg->var_off);
-			true_umax += gen_hi_max(true_reg->var_off);
-		}
-		false_reg->umin_value = max(false_reg->umin_value, false_umin);
-		true_reg->umax_value = min(true_reg->umax_value, true_umax);
+		set_lower_bound(false_reg, val, is_jmp32, opcode == BPF_JGE);
+		set_upper_bound(true_reg, val, is_jmp32, opcode == BPF_JGT);
 		break;
 	}
 	case BPF_JSGE:
@@ -5871,15 +5914,8 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
 	case BPF_JLE:
 	case BPF_JLT:
 	{
-		u64 false_umax = opcode == BPF_JLT ? val    : val - 1;
-		u64 true_umin = opcode == BPF_JLT ? val + 1 : val;
-
-		if (is_jmp32) {
-			false_umax += gen_hi_max(false_reg->var_off);
-			true_umin += gen_hi_min(true_reg->var_off);
-		}
-		false_reg->umax_value = min(false_reg->umax_value, false_umax);
-		true_reg->umin_value = max(true_reg->umin_value, true_umin);
+		set_upper_bound(false_reg, val, is_jmp32, opcode == BPF_JLE);
+		set_lower_bound(true_reg, val, is_jmp32, opcode == BPF_JLT);
 		break;
 	}
 	case BPF_JSLE:
-- 
2.20.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* [PATCH bpf-next 3/3] bpf: Simplify reg_set_min_max_inv handling
  2020-03-30 16:03 [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Daniel Borkmann
  2020-03-30 16:03 ` [PATCH bpf-next 1/3] bpf: Undo incorrect " Daniel Borkmann
  2020-03-30 16:03 ` [PATCH bpf-next 2/3] bpf: Fix tnum constraints for 32-bit comparisons Daniel Borkmann
@ 2020-03-30 16:03 ` Daniel Borkmann
  2020-03-30 19:01 ` [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Alexei Starovoitov
  3 siblings, 0 replies; 5+ messages in thread
From: Daniel Borkmann @ 2020-03-30 16:03 UTC (permalink / raw)
  To: alexei.starovoitov
  Cc: jannh, yhs, john.fastabend, bpf, netdev, Daniel Borkmann

From: Jann Horn <jannh@google.com>

reg_set_min_max_inv() contains exactly the same logic as reg_set_min_max(),
just flipped around. While this makes sense in a cBPF verifier (where ALU
operations are not symmetric), it does not make sense for eBPF.

Replace reg_set_min_max_inv() with a helper that flips the opcode around,
then lets reg_set_min_max() do the complicated work.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 108 +++++++++---------------------------------
 1 file changed, 22 insertions(+), 86 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6fce6f096c16..b55842033073 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5836,7 +5836,7 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
 		break;
 	}
 	default:
-		break;
+		return;
 	}
 
 	__reg_deduce_bounds(false_reg);
@@ -5859,92 +5859,28 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
 				struct bpf_reg_state *false_reg, u64 val,
 				u8 opcode, bool is_jmp32)
 {
-	s64 sval;
-
-	if (__is_pointer_value(false, false_reg))
-		return;
-
-	val = is_jmp32 ? (u32)val : val;
-	sval = is_jmp32 ? (s64)(s32)val : (s64)val;
-
-	switch (opcode) {
-	case BPF_JEQ:
-	case BPF_JNE:
-	{
-		struct bpf_reg_state *reg =
-			opcode == BPF_JEQ ? true_reg : false_reg;
-
-		if (is_jmp32) {
-			u64 old_v = reg->var_off.value;
-			u64 hi_mask = ~0xffffffffULL;
-
-			reg->var_off.value = (old_v & hi_mask) | val;
-			reg->var_off.mask &= hi_mask;
-		} else {
-			__mark_reg_known(reg, val);
-		}
-		break;
-	}
-	case BPF_JSET:
-		false_reg->var_off = tnum_and(false_reg->var_off,
-					      tnum_const(~val));
-		if (is_power_of_2(val))
-			true_reg->var_off = tnum_or(true_reg->var_off,
-						    tnum_const(val));
-		break;
-	case BPF_JGE:
-	case BPF_JGT:
-	{
-		set_lower_bound(false_reg, val, is_jmp32, opcode == BPF_JGE);
-		set_upper_bound(true_reg, val, is_jmp32, opcode == BPF_JGT);
-		break;
-	}
-	case BPF_JSGE:
-	case BPF_JSGT:
-	{
-		s64 false_smin = opcode == BPF_JSGT ? sval    : sval + 1;
-		s64 true_smax = opcode == BPF_JSGT ? sval - 1 : sval;
-
-		if (is_jmp32 && !cmp_val_with_extended_s64(sval, false_reg))
-			break;
-		false_reg->smin_value = max(false_reg->smin_value, false_smin);
-		true_reg->smax_value = min(true_reg->smax_value, true_smax);
-		break;
-	}
-	case BPF_JLE:
-	case BPF_JLT:
-	{
-		set_upper_bound(false_reg, val, is_jmp32, opcode == BPF_JLE);
-		set_lower_bound(true_reg, val, is_jmp32, opcode == BPF_JLT);
-		break;
-	}
-	case BPF_JSLE:
-	case BPF_JSLT:
-	{
-		s64 false_smax = opcode == BPF_JSLT ? sval    : sval - 1;
-		s64 true_smin = opcode == BPF_JSLT ? sval + 1 : sval;
-
-		if (is_jmp32 && !cmp_val_with_extended_s64(sval, false_reg))
-			break;
-		false_reg->smax_value = min(false_reg->smax_value, false_smax);
-		true_reg->smin_value = max(true_reg->smin_value, true_smin);
-		break;
-	}
-	default:
-		break;
-	}
-
-	__reg_deduce_bounds(false_reg);
-	__reg_deduce_bounds(true_reg);
-	/* We might have learned some bits from the bounds. */
-	__reg_bound_offset(false_reg);
-	__reg_bound_offset(true_reg);
-	/* Intersecting with the old var_off might have improved our bounds
-	 * slightly.  e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc),
-	 * then new var_off is (0; 0x7f...fc) which improves our umax.
+	/* How can we transform "a <op> b" into "b <op> a"? */
+	static const u8 opcode_flip[16] = {
+		/* these stay the same */
+		[BPF_JEQ  >> 4] = BPF_JEQ,
+		[BPF_JNE  >> 4] = BPF_JNE,
+		[BPF_JSET >> 4] = BPF_JSET,
+		/* these swap "lesser" and "greater" (L and G in the opcodes) */
+		[BPF_JGE  >> 4] = BPF_JLE,
+		[BPF_JGT  >> 4] = BPF_JLT,
+		[BPF_JLE  >> 4] = BPF_JGE,
+		[BPF_JLT  >> 4] = BPF_JGT,
+		[BPF_JSGE >> 4] = BPF_JSLE,
+		[BPF_JSGT >> 4] = BPF_JSLT,
+		[BPF_JSLE >> 4] = BPF_JSGE,
+		[BPF_JSLT >> 4] = BPF_JSGT
+	};
+	opcode = opcode_flip[opcode >> 4];
+	/* This uses zero as "not present in table"; luckily the zero opcode,
+	 * BPF_JA, can't get here.
 	 */
-	__update_reg_bounds(false_reg);
-	__update_reg_bounds(true_reg);
+	if (opcode)
+		reg_set_min_max(true_reg, false_reg, val, opcode, is_jmp32);
 }
 
 /* Regs are known to be equal, so intersect their min/max/var_off */
-- 
2.20.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling
  2020-03-30 16:03 [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Daniel Borkmann
                   ` (2 preceding siblings ...)
  2020-03-30 16:03 ` [PATCH bpf-next 3/3] bpf: Simplify reg_set_min_max_inv handling Daniel Borkmann
@ 2020-03-30 19:01 ` Alexei Starovoitov
  3 siblings, 0 replies; 5+ messages in thread
From: Alexei Starovoitov @ 2020-03-30 19:01 UTC (permalink / raw)
  To: Daniel Borkmann
  Cc: Jann Horn, Yonghong Song, John Fastabend, bpf, Network Development

On Mon, Mar 30, 2020 at 9:03 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> Fix for the verifier's __reg_bound_offset32() handling, please see individual
> patches for details.

Applied. Thanks

^ permalink raw reply	[flat|nested] 5+ messages in thread

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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-30 16:03 [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Daniel Borkmann
2020-03-30 16:03 ` [PATCH bpf-next 1/3] bpf: Undo incorrect " Daniel Borkmann
2020-03-30 16:03 ` [PATCH bpf-next 2/3] bpf: Fix tnum constraints for 32-bit comparisons Daniel Borkmann
2020-03-30 16:03 ` [PATCH bpf-next 3/3] bpf: Simplify reg_set_min_max_inv handling Daniel Borkmann
2020-03-30 19:01 ` [PATCH bpf-next 0/3] Fix __reg_bound_offset32 handling Alexei Starovoitov

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