[bpf,v2] riscv, bpf: Emit fixed-length instructions for BPF_PSEUDO_FUNC

Commit Message

Pu Lehui Dec. 2, 2022, 9:48 a.m. UTC

From: Pu Lehui <[e-mail]>

For BPF_PSEUDO_FUNC instruction, verifier will refill imm with
correct addresses of bpf_calls and then run last pass of JIT.
Since the emit_imm of RV64 is variable-length, which will emit
appropriate length instructions accorroding to the imm, it may
broke ctx->offset, and lead to unpredictable problem, such as
inaccurate jump. So let's fix it with fixed-length instructions.

Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
Signed-off-by: Pu Lehui <[e-mail]>
Suggested-by: Björn Töpel <[e-mail]>
---
 arch/riscv/net/bpf_jit_comp64.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

Comments

Björn Töpel Dec. 2, 2022, 10:54 a.m. UTC | #1

Pu Lehui <[e-mail]> writes:

> From: Pu Lehui <[e-mail]>
>
> For BPF_PSEUDO_FUNC instruction, verifier will refill imm with
> correct addresses of bpf_calls and then run last pass of JIT.
> Since the emit_imm of RV64 is variable-length, which will emit
> appropriate length instructions accorroding to the imm, it may
> broke ctx->offset, and lead to unpredictable problem, such as
> inaccurate jump. So let's fix it with fixed-length instructions.
>
> Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
> Signed-off-by: Pu Lehui <[e-mail]>
> Suggested-by: Björn Töpel <[e-mail]>
> ---
>  arch/riscv/net/bpf_jit_comp64.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index eb99df41fa33..9723f34f7a06 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -139,6 +139,19 @@ static bool in_auipc_jalr_range(s64 val)
>  		val < ((1L << 31) - (1L << 11));
>  }
>  
> +/* Emit fixed-length instructions for address */
> +static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
> +{
> +	u64 ip = (u64)(ctx->insns + ctx->ninsns);
> +	s64 off = addr - ip;
> +	s64 upper = (off + (1 << 11)) >> 12;
> +	s64 lower = ((off & 0xfff) << 52) >> 52;
> +
> +	emit(rv_auipc(rd, upper), ctx);
> +	emit(rv_addi(rd, rd, lower), ctx);
> +}

Nice! Two instructions are better than 6! :-)

One final thing. Please add a sanity check, that the range is correct,
e.g.:

  if (!(addr && in_auipc_addi_range(off)))
     return -1;

Have a look at emit_jump_and_link().


Thanks!
Björn

Pu Lehui Dec. 6, 2022, 3:37 a.m. UTC | #2

On 2022/12/2 18:54, Björn Töpel wrote:
> Pu Lehui <[e-mail]> writes:
> 
>> From: Pu Lehui <[e-mail]>
>>
>> For BPF_PSEUDO_FUNC instruction, verifier will refill imm with
>> correct addresses of bpf_calls and then run last pass of JIT.
>> Since the emit_imm of RV64 is variable-length, which will emit
>> appropriate length instructions accorroding to the imm, it may
>> broke ctx->offset, and lead to unpredictable problem, such as
>> inaccurate jump. So let's fix it with fixed-length instructions.
>>
>> Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
>> Signed-off-by: Pu Lehui <[e-mail]>
>> Suggested-by: Björn Töpel <[e-mail]>
>> ---
>>   arch/riscv/net/bpf_jit_comp64.c | 20 +++++++++++++++++++-
>>   1 file changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>> index eb99df41fa33..9723f34f7a06 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -139,6 +139,19 @@ static bool in_auipc_jalr_range(s64 val)
>>   		val < ((1L << 31) - (1L << 11));
>>   }
>>   
>> +/* Emit fixed-length instructions for address */
>> +static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
>> +{
>> +	u64 ip = (u64)(ctx->insns + ctx->ninsns);
>> +	s64 off = addr - ip;
>> +	s64 upper = (off + (1 << 11)) >> 12;
>> +	s64 lower = ((off & 0xfff) << 52) >> 52;
>> +
>> +	emit(rv_auipc(rd, upper), ctx);
>> +	emit(rv_addi(rd, rd, lower), ctx);
>> +}
> 
> Nice! Two instructions are better than 6! :-)
> 
> One final thing. Please add a sanity check, that the range is correct,
> e.g.:
> 
>    if (!(addr && in_auipc_addi_range(off)))
>       return -1;
> 

Hi Björn,

Sorry for replying so late. For BPF_PSEUDO_FUNC instruction, verifier 
will set insn[0].imm and insn[1].imm to 1 that make addr to 0x100000001 
before extra pass, and also ctx->insns is NULL in iteration stage, all 
of these make off out of range of AUIPC-ADDI range, and return failed. 
We could add some special handling at different stages, but that seems a 
little weird. By the way, I do not really like emit_addr function with 
return value.

While a proper address is at least 2B alignment, and the valid address 
is from 0xffffffff00000000 to 0xffffffffffffffff, we can make address 
shifed 1 place to right, and addr >> 1 will always in the range of 
AUIPC-ADDI range. We can get rid of the range detection. The 
implementation is as follows:

static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
{
          s64 imm = addr >> 1;
          s64 upper = (imm + (1 << 11)) >> 12;
          s64 lower = imm & 0xfff;

          emit(rv_lui(rd, upper), ctx);
          emit(rv_addi(rd, rd, lower), ctx);
          emit(rv_slli(rd, rd, 1), ctx);
}

What do you think?

Regards,
Lehui

> Have a look at emit_jump_and_link().
> 
> 
> Thanks!
> Björn

Björn Töpel Dec. 6, 2022, 7:55 a.m. UTC | #3

Pu Lehui <[e-mail]> writes:

> Sorry for replying so late. For BPF_PSEUDO_FUNC instruction, verifier 
> will set insn[0].imm and insn[1].imm to 1 that make addr to 0x100000001 
> before extra pass, and also ctx->insns is NULL in iteration stage, all 
> of these make off out of range of AUIPC-ADDI range, and return failed. 
> We could add some special handling at different stages, but that seems a 
> little weird. By the way, I do not really like emit_addr function with 
> return value.

My rational is that *if* for some reason the jit is passed an address
that auipc/addi can't represent, we'd like to catch that and not emit
broken code.

> While a proper address is at least 2B alignment, and the valid address 
> is from 0xffffffff00000000 to 0xffffffffffffffff, we can make address 
> shifed 1 place to right, and addr >> 1 will always in the range of 
> AUIPC-ADDI range. We can get rid of the range detection. The 
> implementation is as follows:
>
> static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
> {
>           s64 imm = addr >> 1;
>           s64 upper = (imm + (1 << 11)) >> 12;
>           s64 lower = imm & 0xfff;
>
>           emit(rv_lui(rd, upper), ctx);
>           emit(rv_addi(rd, rd, lower), ctx);
>           emit(rv_slli(rd, rd, 1), ctx);
> }
>
> What do you think?

That's a code generation penalty, instead of catching it at code
gen. Don't like! :-) I much prefer the auipc/addi version.

What do you think about the diff (on-top of your work) below?

--8<--
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index aa9410eef77c..7acaf28cb3be 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -137,15 +137,21 @@ static bool in_auipc_jalr_range(s64 val)
 }
 
 /* Emit fixed-length instructions for address */
-static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
+static int emit_addr(u8 rd, u64 addr, bool extra_pass, struct rv_jit_context *ctx)
 {
 	u64 ip = (u64)(ctx->insns + ctx->ninsns);
 	s64 off = addr - ip;
 	s64 upper = (off + (1 << 11)) >> 12;
 	s64 lower = ((off & 0xfff) << 52) >> 52;
 
+	if (extra_pass && !in_auipc_jalr_range(off)) {
+		pr_err("bpf-jit: target offset 0x%llx is out of range\n", off);
+		return -ERANGE;
+	}
+
 	emit(rv_auipc(rd, upper), ctx);
 	emit(rv_addi(rd, rd, lower), ctx);
+	return 0;
 }
 
 /* Emit variable-length instructions for 32-bit and 64-bit imm */
@@ -1061,13 +1067,17 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 	{
 		struct bpf_insn insn1 = insn[1];
 		u64 imm64;
+		int ret;
 
 		imm64 = (u64)insn1.imm << 32 | (u32)imm;
-		if (bpf_pseudo_func(insn))
+		if (bpf_pseudo_func(insn)) {
 			/* fixed-length insns for extra jit pass */
-			emit_addr(rd, imm64, ctx);
-		else
+			ret = emit_addr(rd, imm64, extra_pass, ctx);
+			if (ret)
+				return ret;
+		} else {
 			emit_imm(rd, imm64, ctx);
+		}
 
 		return 1;
 	}

--8<--

Wouldn't that work?


Björn

Pu Lehui Dec. 6, 2022, 8:16 a.m. UTC | #4

On 2022/12/6 15:55, Björn Töpel wrote:
> Pu Lehui <[e-mail]> writes:
> 
>> Sorry for replying so late. For BPF_PSEUDO_FUNC instruction, verifier
>> will set insn[0].imm and insn[1].imm to 1 that make addr to 0x100000001
>> before extra pass, and also ctx->insns is NULL in iteration stage, all
>> of these make off out of range of AUIPC-ADDI range, and return failed.
>> We could add some special handling at different stages, but that seems a
>> little weird. By the way, I do not really like emit_addr function with
>> return value.
> 
> My rational is that *if* for some reason the jit is passed an address
> that auipc/addi can't represent, we'd like to catch that and not emit
> broken code.
> 
>> While a proper address is at least 2B alignment, and the valid address
>> is from 0xffffffff00000000 to 0xffffffffffffffff, we can make address
>> shifed 1 place to right, and addr >> 1 will always in the range of
>> AUIPC-ADDI range. We can get rid of the range detection. The
>> implementation is as follows:
>>
>> static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
>> {
>>            s64 imm = addr >> 1;
>>            s64 upper = (imm + (1 << 11)) >> 12;
>>            s64 lower = imm & 0xfff;
>>
>>            emit(rv_lui(rd, upper), ctx);
>>            emit(rv_addi(rd, rd, lower), ctx);
>>            emit(rv_slli(rd, rd, 1), ctx);
>> }
>>
>> What do you think?
> 
> That's a code generation penalty, instead of catching it at code
> gen. Don't like! :-) I much prefer the auipc/addi version.
> 
> What do you think about the diff (on-top of your work) below?
> 
> --8<--
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index aa9410eef77c..7acaf28cb3be 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -137,15 +137,21 @@ static bool in_auipc_jalr_range(s64 val)
>   }
>   
>   /* Emit fixed-length instructions for address */
> -static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
> +static int emit_addr(u8 rd, u64 addr, bool extra_pass, struct rv_jit_context *ctx)
>   {
>   	u64 ip = (u64)(ctx->insns + ctx->ninsns);
>   	s64 off = addr - ip;
>   	s64 upper = (off + (1 << 11)) >> 12;
>   	s64 lower = ((off & 0xfff) << 52) >> 52;
>   
> +	if (extra_pass && !in_auipc_jalr_range(off)) {
> +		pr_err("bpf-jit: target offset 0x%llx is out of range\n", off);
> +		return -ERANGE;
> +	}
> +
>   	emit(rv_auipc(rd, upper), ctx);
>   	emit(rv_addi(rd, rd, lower), ctx);
> +	return 0;
>   }
>   
>   /* Emit variable-length instructions for 32-bit and 64-bit imm */
> @@ -1061,13 +1067,17 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>   	{
>   		struct bpf_insn insn1 = insn[1];
>   		u64 imm64;
> +		int ret;
>   
>   		imm64 = (u64)insn1.imm << 32 | (u32)imm;
> -		if (bpf_pseudo_func(insn))
> +		if (bpf_pseudo_func(insn)) {
>   			/* fixed-length insns for extra jit pass */
> -			emit_addr(rd, imm64, ctx);
> -		else
> +			ret = emit_addr(rd, imm64, extra_pass, ctx);
> +			if (ret)
> +				return ret;
> +		} else {
>   			emit_imm(rd, imm64, ctx);
> +		}
>   
>   		return 1;
>   	}
> 
> --8<--
> 
> Wouldn't that work?
> 

It definitely works. But auipc+addi may be some holes, while 
lui+addi+slli support all the address of kernel and module. And this 
might be help for the future feature porting.

> 
> Björn

Björn Töpel Dec. 6, 2022, 8:42 a.m. UTC | #5

Pu Lehui <[e-mail]> writes:

>> Wouldn't that work?
>> 
>
> It definitely works. But auipc+addi may be some holes, while 
> lui+addi+slli support all the address of kernel and module. And this 
> might be help for the future feature porting.

We're already using auipc/jalr for calls, and I'd say it *very* unlikely
that we'll hit the non-covered range. I'd say go with auipc/addi +
error, and we can change if this really is a problem.

Pu Lehui Dec. 6, 2022, 8:49 a.m. UTC | #6

On 2022/12/6 16:42, Björn Töpel wrote:
> Pu Lehui <[e-mail]> writes:
> 
>>> Wouldn't that work?
>>>
>>
>> It definitely works. But auipc+addi may be some holes, while
>> lui+addi+slli support all the address of kernel and module. And this
>> might be help for the future feature porting.
> 
> We're already using auipc/jalr for calls, and I'd say it *very* unlikely
> that we'll hit the non-covered range. I'd say go with auipc/addi +
> error, and we can change if this really is a problem.

Well, thank you for your patience, will send new soon.

Patch

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index eb99df41fa33..9723f34f7a06 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -139,6 +139,19 @@  static bool in_auipc_jalr_range(s64 val)
 		val < ((1L << 31) - (1L << 11));
 }
 
+/* Emit fixed-length instructions for address */
+static void emit_addr(u8 rd, u64 addr, struct rv_jit_context *ctx)
+{
+	u64 ip = (u64)(ctx->insns + ctx->ninsns);
+	s64 off = addr - ip;
+	s64 upper = (off + (1 << 11)) >> 12;
+	s64 lower = ((off & 0xfff) << 52) >> 52;
+
+	emit(rv_auipc(rd, upper), ctx);
+	emit(rv_addi(rd, rd, lower), ctx);
+}
+
+/* Emit variable-length instructions for 32-bit and 64-bit imm */
 static void emit_imm(u8 rd, s64 val, struct rv_jit_context *ctx)
 {
 	/* Note that the immediate from the add is sign-extended,
@@ -1053,7 +1066,12 @@  int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 		u64 imm64;
 
 		imm64 = (u64)insn1.imm << 32 | (u32)imm;
-		emit_imm(rd, imm64, ctx);
+		if (bpf_pseudo_func(insn))
+			/* fixed-length insns for extra jit pass */
+			emit_addr(rd, imm64, ctx);
+		else
+			emit_imm(rd, imm64, ctx);
+
 		return 1;
 	}