diff mbox series

[RFC] bpf: handle 32-bit zext during constant blinding

Message ID 20190813171018.28221-1-naveen.n.rao@linux.vnet.ibm.com
State RFC
Delegated to: BPF Maintainers
Headers show
Series [RFC] bpf: handle 32-bit zext during constant blinding | expand

Commit Message

Naveen N. Rao Aug. 13, 2019, 5:10 p.m. UTC 
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(-)

Comments

Naveen N. Rao Aug. 21, 2019, 8:30 a.m. UTC | #1 
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
Jiong Wang Aug. 21, 2019, 9:05 a.m. UTC | #2 
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
Michael Ellerman Aug. 21, 2019, 10:25 a.m. UTC | #3 
"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
Jiong Wang Aug. 21, 2019, 10:55 a.m. UTC | #4 
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
Naveen N. Rao Aug. 21, 2019, 7:12 p.m. UTC | #5 
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
diff mbox series

Patch

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;