* [RFC PATCH] bpf: handle 32-bit zext during constant blinding
@ 2019-08-13 17:10 Naveen N. Rao
2019-08-21 8:30 ` Naveen N. Rao
2019-08-21 10:25 ` Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding) Michael Ellerman
0 siblings, 2 replies; 6+ messages in thread
From: Naveen N. Rao @ 2019-08-13 17:10 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Jiong Wang
Cc: bpf, linuxppc-dev, linux-kernel, netdev
Since BPF constant blinding is performed after the verifier pass, there
are certain ALU32 instructions inserted which don't have a corresponding
zext instruction inserted after. This is causing a kernel oops on
powerpc and can be reproduced by running 'test_cgroup_storage' with
bpf_jit_harden=2.
Fix this by emitting BPF_ZEXT during constant blinding if
prog->aux->verifier_zext is set.
Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result")
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
This approach (the location where zext is being introduced below, in
particular) works for powerpc, but I am not entirely sure if this is
sufficient for other architectures as well. This is broken on v5.3-rc4.
- Naveen
kernel/bpf/core.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 8191a7db2777..d84146e6fd9e 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -890,7 +890,8 @@ int bpf_jit_get_func_addr(const struct bpf_prog *prog,
static int bpf_jit_blind_insn(const struct bpf_insn *from,
const struct bpf_insn *aux,
- struct bpf_insn *to_buff)
+ struct bpf_insn *to_buff,
+ bool emit_zext)
{
struct bpf_insn *to = to_buff;
u32 imm_rnd = get_random_int();
@@ -939,6 +940,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
*to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
*to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
*to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX);
+ if (emit_zext)
+ *to++ = BPF_ZEXT_REG(from->dst_reg);
break;
case BPF_ALU64 | BPF_ADD | BPF_K:
@@ -992,6 +995,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
off -= 2;
*to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
*to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
+ if (emit_zext) {
+ *to++ = BPF_ZEXT_REG(BPF_REG_AX);
+ off--;
+ }
*to++ = BPF_JMP32_REG(from->code, from->dst_reg, BPF_REG_AX,
off);
break;
@@ -1005,6 +1012,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */
*to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm);
*to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
+ if (emit_zext)
+ *to++ = BPF_ZEXT_REG(BPF_REG_AX);
*to++ = BPF_ALU64_REG(BPF_OR, aux[0].dst_reg, BPF_REG_AX);
break;
@@ -1088,7 +1097,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
insn[1].code == 0)
memcpy(aux, insn, sizeof(aux));
- rewritten = bpf_jit_blind_insn(insn, aux, insn_buff);
+ rewritten = bpf_jit_blind_insn(insn, aux, insn_buff,
+ clone->aux->verifier_zext);
if (!rewritten)
continue;
--
2.22.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding
2019-08-13 17:10 [RFC PATCH] bpf: handle 32-bit zext during constant blinding Naveen N. Rao
@ 2019-08-21 8:30 ` Naveen N. Rao
2019-08-21 9:05 ` Jiong Wang
2019-08-21 10:25 ` Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding) Michael Ellerman
1 sibling, 1 reply; 6+ messages in thread
From: Naveen N. Rao @ 2019-08-21 8:30 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Jiong Wang
Cc: bpf, linuxppc-dev, linux-kernel, netdev
Naveen N. Rao wrote:
> Since BPF constant blinding is performed after the verifier pass, there
> are certain ALU32 instructions inserted which don't have a corresponding
> zext instruction inserted after. This is causing a kernel oops on
> powerpc and can be reproduced by running 'test_cgroup_storage' with
> bpf_jit_harden=2.
>
> Fix this by emitting BPF_ZEXT during constant blinding if
> prog->aux->verifier_zext is set.
>
> Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result")
> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> This approach (the location where zext is being introduced below, in
> particular) works for powerpc, but I am not entirely sure if this is
> sufficient for other architectures as well. This is broken on v5.3-rc4.
Alexie, Daniel, Jiong,
Any feedback on this?
- Naveen
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding
2019-08-21 8:30 ` Naveen N. Rao
@ 2019-08-21 9:05 ` Jiong Wang
0 siblings, 0 replies; 6+ messages in thread
From: Jiong Wang @ 2019-08-21 9:05 UTC (permalink / raw)
To: Naveen N. Rao
Cc: Daniel Borkmann, Jiong Wang, linux-kernel, netdev, bpf,
linuxppc-dev, Alexei Starovoitov
Naveen N. Rao writes:
> Naveen N. Rao wrote:
>> Since BPF constant blinding is performed after the verifier pass, there
>> are certain ALU32 instructions inserted which don't have a corresponding
>> zext instruction inserted after. This is causing a kernel oops on
>> powerpc and can be reproduced by running 'test_cgroup_storage' with
>> bpf_jit_harden=2.
>>
>> Fix this by emitting BPF_ZEXT during constant blinding if
>> prog->aux->verifier_zext is set.
>>
>> Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result")
>> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>> ---
>> This approach (the location where zext is being introduced below, in
>> particular) works for powerpc, but I am not entirely sure if this is
>> sufficient for other architectures as well. This is broken on v5.3-rc4.
>
> Alexie, Daniel, Jiong,
> Any feedback on this?
The fix on BPF_LD | BPF_IMM | BPF_DW looks correct to me, but the two other
places looks to me is unnecessary, as those destinations are exposed to
external and if they are used as 64-bit then there will be zext inserted
for them.
Have you verified removing those two fixes will still cause the bug?
Regards,
Jiong
>
> - Naveen
^ permalink raw reply [flat|nested] 6+ messages in thread
* Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding)
2019-08-13 17:10 [RFC PATCH] bpf: handle 32-bit zext during constant blinding Naveen N. Rao
2019-08-21 8:30 ` Naveen N. Rao
@ 2019-08-21 10:25 ` Michael Ellerman
2019-08-21 10:55 ` Jiong Wang
1 sibling, 1 reply; 6+ messages in thread
From: Michael Ellerman @ 2019-08-21 10:25 UTC (permalink / raw)
To: Naveen N. Rao, Alexei Starovoitov, Daniel Borkmann, Jiong Wang
Cc: netdev, bpf, linuxppc-dev, linux-kernel
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
> Since BPF constant blinding is performed after the verifier pass, there
> are certain ALU32 instructions inserted which don't have a corresponding
> zext instruction inserted after. This is causing a kernel oops on
> powerpc and can be reproduced by running 'test_cgroup_storage' with
> bpf_jit_harden=2.
>
> Fix this by emitting BPF_ZEXT during constant blinding if
> prog->aux->verifier_zext is set.
>
> Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result")
> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> This approach (the location where zext is being introduced below, in
> particular) works for powerpc, but I am not entirely sure if this is
> sufficient for other architectures as well. This is broken on v5.3-rc4.
Any comment on this?
This is a regression in v5.3, which results in a kernel crash, it would
be nice to get it fixed before the release please?
cheers
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 8191a7db2777..d84146e6fd9e 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -890,7 +890,8 @@ int bpf_jit_get_func_addr(const struct bpf_prog *prog,
>
> static int bpf_jit_blind_insn(const struct bpf_insn *from,
> const struct bpf_insn *aux,
> - struct bpf_insn *to_buff)
> + struct bpf_insn *to_buff,
> + bool emit_zext)
> {
> struct bpf_insn *to = to_buff;
> u32 imm_rnd = get_random_int();
> @@ -939,6 +940,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
> *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
> *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
> *to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX);
> + if (emit_zext)
> + *to++ = BPF_ZEXT_REG(from->dst_reg);
> break;
>
> case BPF_ALU64 | BPF_ADD | BPF_K:
> @@ -992,6 +995,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
> off -= 2;
> *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
> *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
> + if (emit_zext) {
> + *to++ = BPF_ZEXT_REG(BPF_REG_AX);
> + off--;
> + }
> *to++ = BPF_JMP32_REG(from->code, from->dst_reg, BPF_REG_AX,
> off);
> break;
> @@ -1005,6 +1012,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
> case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */
> *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm);
> *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
> + if (emit_zext)
> + *to++ = BPF_ZEXT_REG(BPF_REG_AX);
> *to++ = BPF_ALU64_REG(BPF_OR, aux[0].dst_reg, BPF_REG_AX);
> break;
>
> @@ -1088,7 +1097,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
> insn[1].code == 0)
> memcpy(aux, insn, sizeof(aux));
>
> - rewritten = bpf_jit_blind_insn(insn, aux, insn_buff);
> + rewritten = bpf_jit_blind_insn(insn, aux, insn_buff,
> + clone->aux->verifier_zext);
> if (!rewritten)
> continue;
>
> --
> 2.22.0
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding)
2019-08-21 10:25 ` Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding) Michael Ellerman
@ 2019-08-21 10:55 ` Jiong Wang
2019-08-21 19:12 ` Naveen N. Rao
0 siblings, 1 reply; 6+ messages in thread
From: Jiong Wang @ 2019-08-21 10:55 UTC (permalink / raw)
To: Michael Ellerman
Cc: Daniel Borkmann, Jiong Wang, netdev, linux-kernel,
Alexei Starovoitov, Naveen N. Rao, linuxppc-dev, bpf
Michael Ellerman writes:
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
>> Since BPF constant blinding is performed after the verifier pass, there
>> are certain ALU32 instructions inserted which don't have a corresponding
>> zext instruction inserted after. This is causing a kernel oops on
>> powerpc and can be reproduced by running 'test_cgroup_storage' with
>> bpf_jit_harden=2.
>>
>> Fix this by emitting BPF_ZEXT during constant blinding if
>> prog->aux->verifier_zext is set.
>>
>> Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result")
>> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>> ---
>> This approach (the location where zext is being introduced below, in
>> particular) works for powerpc, but I am not entirely sure if this is
>> sufficient for other architectures as well. This is broken on v5.3-rc4.
>
> Any comment on this?
Have commented on https://marc.info/?l=linux-netdev&m=156637836024743&w=2
The fix looks correct to me on "BPF_LD | BPF_IMM | BPF_DW", but looks
unnecessary on two other places. It would be great if you or Naveen could
confirm it.
Thanks.
Regards,
Jiong
> This is a regression in v5.3, which results in a kernel crash, it would
> be nice to get it fixed before the release please?
>
> cheers
>
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 8191a7db2777..d84146e6fd9e 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -890,7 +890,8 @@ int bpf_jit_get_func_addr(const struct bpf_prog *prog,
>>
>> static int bpf_jit_blind_insn(const struct bpf_insn *from,
>> const struct bpf_insn *aux,
>> - struct bpf_insn *to_buff)
>> + struct bpf_insn *to_buff,
>> + bool emit_zext)
>> {
>> struct bpf_insn *to = to_buff;
>> u32 imm_rnd = get_random_int();
>> @@ -939,6 +940,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
>> *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
>> *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
>> *to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX);
>> + if (emit_zext)
>> + *to++ = BPF_ZEXT_REG(from->dst_reg);
>> break;
>>
>> case BPF_ALU64 | BPF_ADD | BPF_K:
>> @@ -992,6 +995,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
>> off -= 2;
>> *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
>> *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
>> + if (emit_zext) {
>> + *to++ = BPF_ZEXT_REG(BPF_REG_AX);
>> + off--;
>> + }
>> *to++ = BPF_JMP32_REG(from->code, from->dst_reg, BPF_REG_AX,
>> off);
>> break;
>> @@ -1005,6 +1012,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
>> case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */
>> *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm);
>> *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
>> + if (emit_zext)
>> + *to++ = BPF_ZEXT_REG(BPF_REG_AX);
>> *to++ = BPF_ALU64_REG(BPF_OR, aux[0].dst_reg, BPF_REG_AX);
>> break;
>>
>> @@ -1088,7 +1097,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
>> insn[1].code == 0)
>> memcpy(aux, insn, sizeof(aux));
>>
>> - rewritten = bpf_jit_blind_insn(insn, aux, insn_buff);
>> + rewritten = bpf_jit_blind_insn(insn, aux, insn_buff,
>> + clone->aux->verifier_zext);
>> if (!rewritten)
>> continue;
>>
>> --
>> 2.22.0
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding)
2019-08-21 10:55 ` Jiong Wang
@ 2019-08-21 19:12 ` Naveen N. Rao
0 siblings, 0 replies; 6+ messages in thread
From: Naveen N. Rao @ 2019-08-21 19:12 UTC (permalink / raw)
To: Jiong Wang, Michael Ellerman
Cc: Daniel Borkmann, netdev, linux-kernel, bpf, linuxppc-dev,
Alexei Starovoitov
Jiong Wang wrote:
>
> Michael Ellerman writes:
>
>> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
>>> Since BPF constant blinding is performed after the verifier pass, there
>>> are certain ALU32 instructions inserted which don't have a corresponding
>>> zext instruction inserted after. This is causing a kernel oops on
>>> powerpc and can be reproduced by running 'test_cgroup_storage' with
>>> bpf_jit_harden=2.
>>>
>>> Fix this by emitting BPF_ZEXT during constant blinding if
>>> prog->aux->verifier_zext is set.
>>>
>>> Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result")
>>> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
>>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>>> ---
>>> This approach (the location where zext is being introduced below, in
>>> particular) works for powerpc, but I am not entirely sure if this is
>>> sufficient for other architectures as well. This is broken on v5.3-rc4.
>>
>> Any comment on this?
>
> Have commented on https://marc.info/?l=linux-netdev&m=156637836024743&w=2
>
> The fix looks correct to me on "BPF_LD | BPF_IMM | BPF_DW", but looks
> unnecessary on two other places. It would be great if you or Naveen could
> confirm it.
Jiong,
Thanks for the review. I can now see why the other two changes are not
necessary. I will post a follow-on patch.
Thanks!
- Naveen
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-08-21 19:14 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2019-08-13 17:10 [RFC PATCH] bpf: handle 32-bit zext during constant blinding Naveen N. Rao
2019-08-21 8:30 ` Naveen N. Rao
2019-08-21 9:05 ` Jiong Wang
2019-08-21 10:25 ` Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding) Michael Ellerman
2019-08-21 10:55 ` Jiong Wang
2019-08-21 19:12 ` Naveen N. Rao
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