| Message ID | 1544862880-23291-1-git-send-email-jiong.wang@netronome.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf-next] bpf: correct slot_type marking logic to allow more stack slot sharing | expand |
On 12/15/2018 09:34 AM, Jiong Wang wrote: > 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>
On Sat, Dec 15, 2018 at 03:34:40AM -0500, Jiong Wang wrote: > 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> Applied, Thanks
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8b511a4..352183b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1220,6 +1220,10 @@ 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 @@ -1237,6 +1241,7 @@ 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; diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index a08c67c..51eea7f 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -1001,15 +1001,45 @@ 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 = "corrupted spill", + .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", + .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", .insns = { BPF_STX_MEM(BPF_B, BPF_REG_10, -1, -1),