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bpf: correct slot_type marking logic to allow more stack slot sharing 

Verifier is supposed to support sharing stack slot allocated to ptr with
SCALAR_VALUE for privileged program. However this doesn't happen for some
cases.

The reason is verifier is not clearing slot_type STACK_SPILL for all bytes,
it only clears part of them, while verifier is using:

  slot_type[0] == STACK_SPILL

as a convention to check one slot is ptr type.

So, the consequence of partial clearing slot_type is verifier could treat a
partially overridden ptr slot, which should now be a SCALAR_VALUE slot,
still as ptr slot, and rejects some valid programs.

Before this patch, test_xdp_noinline.o under bpf selftests, bpf_lxc.o and
bpf_netdev.o under Cilium bpf repo, when built with -mattr=+alu32 are
rejected due to this issue. After this patch, they all accepted.

There is no processed insn number change before and after this patch on
Cilium bpf programs.

Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jiong Wang 2018-12-15 03:34:40 -05:00 committed by Alexei Starovoitov
parent a38d1107f9
commit 0bae2d4d62
2 changed files with 38 additions and 3 deletions
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5
kernel/bpf/verifier.c
View File

@ -1286,6 +1286,10 @@ static int check_stack_write(struct bpf_verifier_env *env,
/* regular write of data into stack destroys any spilled ptr */
state->stack[spi].spilled_ptr.type = NOT_INIT;
/* Mark slots as STACK_MISC if they belonged to spilled ptr. */
if (state->stack[spi].slot_type[0] == STACK_SPILL)
for (i = 0; i < BPF_REG_SIZE; i++)
state->stack[spi].slot_type[i] = STACK_MISC;
/* only mark the slot as written if all 8 bytes were written
* otherwise read propagation may incorrectly stop too soon
@ -1303,6 +1307,7 @@ static int check_stack_write(struct bpf_verifier_env *env,
register_is_null(&cur->regs[value_regno]))
type = STACK_ZERO;
/* Mark slots affected by this stack write. */
for (i = 0; i < size; i++)
state->stack[spi].slot_type[(slot - i) % BPF_REG_SIZE] =
type;

36
tools/testing/selftests/bpf/test_verifier.c
View File

@ -1001,13 +1001,43 @@ static struct bpf_test tests[] = {
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
/* mess up with R1 pointer on stack */
BPF_ST_MEM(BPF_B, BPF_REG_10, -7, 0x23),
/* fill back into R0 should fail */
/* fill back into R0 is fine for priv.
* R0 now becomes SCALAR_VALUE.
*/
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
/* Load from R0 should fail. */
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 8),
BPF_EXIT_INSN(),
},
.errstr_unpriv = "attempt to corrupt spilled",
.errstr = "R0 invalid mem access 'inv",
.result = REJECT,
},
{
"check corrupted spill/fill, LSB",
.insns = {
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
BPF_ST_MEM(BPF_H, BPF_REG_10, -8, 0xcafe),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
BPF_EXIT_INSN(),
},
.errstr_unpriv = "attempt to corrupt spilled",
.errstr = "corrupted spill",
.result = REJECT,
.result_unpriv = REJECT,
.result = ACCEPT,
.retval = POINTER_VALUE,
},
{
"check corrupted spill/fill, MSB",
.insns = {
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 0x12345678),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
BPF_EXIT_INSN(),
},
.errstr_unpriv = "attempt to corrupt spilled",
.result_unpriv = REJECT,
.result = ACCEPT,
.retval = POINTER_VALUE,
},
{
"invalid src register in STX",