[1/2] powerpc/bpf: Fix detecting BPF atomic instructions

Commit Message

Naveen N. Rao July 1, 2021, 3:08 p.m. UTC

Commit 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other
atomics in .imm") converted BPF_XADD to BPF_ATOMIC and added a way to
distinguish instructions based on the immediate field. Existing JIT
implementations were updated to check for the immediate field and to
reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH)
in the immediate field.

However, the check added to powerpc64 JIT did not look at the correct
BPF instruction. Due to this, such programs would be accepted and
incorrectly JIT'ed resulting in soft lockups, as seen with the atomic
bounds test. Fix this by looking at the correct immediate value.

Fixes: 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other atomics in .imm")
Reported-by: Jiri Olsa <[e-mail]>
Tested-by: Jiri Olsa <[e-mail]>
Signed-off-by: Naveen N. Rao <[e-mail]>
---
Hi Jiri,
FYI: I made a small change in this patch -- using 'imm' directly, rather 
than insn[i].imm. I've still added your Tested-by since this shouldn't 
impact the fix in any way.

- Naveen


 arch/powerpc/net/bpf_jit_comp64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Alexei Starovoitov July 1, 2021, 4:03 p.m. UTC | #1

On Thu, Jul 1, 2021 at 8:09 AM Naveen N. Rao
<[e-mail]> wrote:
>
> Commit 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other
> atomics in .imm") converted BPF_XADD to BPF_ATOMIC and added a way to
> distinguish instructions based on the immediate field. Existing JIT
> implementations were updated to check for the immediate field and to
> reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH)
> in the immediate field.
>
> However, the check added to powerpc64 JIT did not look at the correct
> BPF instruction. Due to this, such programs would be accepted and
> incorrectly JIT'ed resulting in soft lockups, as seen with the atomic
> bounds test. Fix this by looking at the correct immediate value.
>
> Fixes: 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other atomics in .imm")
> Reported-by: Jiri Olsa <[e-mail]>
> Tested-by: Jiri Olsa <[e-mail]>
> Signed-off-by: Naveen N. Rao <[e-mail]>
> ---
> Hi Jiri,
> FYI: I made a small change in this patch -- using 'imm' directly, rather
> than insn[i].imm. I've still added your Tested-by since this shouldn't
> impact the fix in any way.
>
> - Naveen

Excellent debugging! You guys are awesome.
How do you want this fix routed? via bpf tree?

Naveen N. Rao July 1, 2021, 7:32 p.m. UTC | #2

Alexei Starovoitov wrote:
> On Thu, Jul 1, 2021 at 8:09 AM Naveen N. Rao
> <[e-mail]> wrote:
>>
>> Commit 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other
>> atomics in .imm") converted BPF_XADD to BPF_ATOMIC and added a way to
>> distinguish instructions based on the immediate field. Existing JIT
>> implementations were updated to check for the immediate field and to
>> reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH)
>> in the immediate field.
>>
>> However, the check added to powerpc64 JIT did not look at the correct
>> BPF instruction. Due to this, such programs would be accepted and
>> incorrectly JIT'ed resulting in soft lockups, as seen with the atomic
>> bounds test. Fix this by looking at the correct immediate value.
>>
>> Fixes: 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other atomics in .imm")
>> Reported-by: Jiri Olsa <[e-mail]>
>> Tested-by: Jiri Olsa <[e-mail]>
>> Signed-off-by: Naveen N. Rao <[e-mail]>
>> ---
>> Hi Jiri,
>> FYI: I made a small change in this patch -- using 'imm' directly, rather
>> than insn[i].imm. I've still added your Tested-by since this shouldn't
>> impact the fix in any way.
>>
>> - Naveen
> 
> Excellent debugging! You guys are awesome.

Thanks. Jiri and Brendan did the bulk of the work :)

> How do you want this fix routed? via bpf tree?

Michael has a few BPF patches queued up in powerpc tree for v5.14, so it 
might be easier to take these patches through the powerpc tree unless he 
feels otherwise. Michael?

This also needs to be tagged for stable:
Cc: [e-mail] # 5.12+


- Naveen

Alexei Starovoitov July 1, 2021, 7:33 p.m. UTC | #3

On Thu, Jul 1, 2021 at 12:32 PM Naveen N. Rao
<[e-mail]> wrote:
>
> Alexei Starovoitov wrote:
> > On Thu, Jul 1, 2021 at 8:09 AM Naveen N. Rao
> > <[e-mail]> wrote:
> >>
> >> Commit 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other
> >> atomics in .imm") converted BPF_XADD to BPF_ATOMIC and added a way to
> >> distinguish instructions based on the immediate field. Existing JIT
> >> implementations were updated to check for the immediate field and to
> >> reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH)
> >> in the immediate field.
> >>
> >> However, the check added to powerpc64 JIT did not look at the correct
> >> BPF instruction. Due to this, such programs would be accepted and
> >> incorrectly JIT'ed resulting in soft lockups, as seen with the atomic
> >> bounds test. Fix this by looking at the correct immediate value.
> >>
> >> Fixes: 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other atomics in .imm")
> >> Reported-by: Jiri Olsa <[e-mail]>
> >> Tested-by: Jiri Olsa <[e-mail]>
> >> Signed-off-by: Naveen N. Rao <[e-mail]>
> >> ---
> >> Hi Jiri,
> >> FYI: I made a small change in this patch -- using 'imm' directly, rather
> >> than insn[i].imm. I've still added your Tested-by since this shouldn't
> >> impact the fix in any way.
> >>
> >> - Naveen
> >
> > Excellent debugging! You guys are awesome.
>
> Thanks. Jiri and Brendan did the bulk of the work :)
>
> > How do you want this fix routed? via bpf tree?
>
> Michael has a few BPF patches queued up in powerpc tree for v5.14, so it
> might be easier to take these patches through the powerpc tree unless he
> feels otherwise. Michael?

Works for me. Thanks!

Jiri Olsa July 2, 2021, 10:26 a.m. UTC | #4

On Thu, Jul 01, 2021 at 08:38:58PM +0530, Naveen N. Rao wrote:
> Commit 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other
> atomics in .imm") converted BPF_XADD to BPF_ATOMIC and added a way to
> distinguish instructions based on the immediate field. Existing JIT
> implementations were updated to check for the immediate field and to
> reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH)
> in the immediate field.
> 
> However, the check added to powerpc64 JIT did not look at the correct
> BPF instruction. Due to this, such programs would be accepted and
> incorrectly JIT'ed resulting in soft lockups, as seen with the atomic
> bounds test. Fix this by looking at the correct immediate value.
> 
> Fixes: 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other atomics in .imm")
> Reported-by: Jiri Olsa <[e-mail]>
> Tested-by: Jiri Olsa <[e-mail]>
> Signed-off-by: Naveen N. Rao <[e-mail]>
> ---
> Hi Jiri,
> FYI: I made a small change in this patch -- using 'imm' directly, rather 
> than insn[i].imm. I've still added your Tested-by since this shouldn't 
> impact the fix in any way.

yep, it works nicely

thanks
jirka

> 
> - Naveen
> 
> 
>  arch/powerpc/net/bpf_jit_comp64.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 5cad5b5a7e9774..de8595880feec6 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -667,7 +667,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>  		 * BPF_STX ATOMIC (atomic ops)
>  		 */
>  		case BPF_STX | BPF_ATOMIC | BPF_W:
> -			if (insn->imm != BPF_ADD) {
> +			if (imm != BPF_ADD) {
>  				pr_err_ratelimited(
>  					"eBPF filter atomic op code %02x (@%d) unsupported\n",
>  					code, i);
> @@ -689,7 +689,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>  			PPC_BCC_SHORT(COND_NE, tmp_idx);
>  			break;
>  		case BPF_STX | BPF_ATOMIC | BPF_DW:
> -			if (insn->imm != BPF_ADD) {
> +			if (imm != BPF_ADD) {
>  				pr_err_ratelimited(
>  					"eBPF filter atomic op code %02x (@%d) unsupported\n",
>  					code, i);
> -- 
> 2.31.1
>

Patch

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 5cad5b5a7e9774..de8595880feec6 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -667,7 +667,7 @@  int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 		 * BPF_STX ATOMIC (atomic ops)
 		 */
 		case BPF_STX | BPF_ATOMIC | BPF_W:
-			if (insn->imm != BPF_ADD) {
+			if (imm != BPF_ADD) {
 				pr_err_ratelimited(
 					"eBPF filter atomic op code %02x (@%d) unsupported\n",
 					code, i);
@@ -689,7 +689,7 @@  int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 			PPC_BCC_SHORT(COND_NE, tmp_idx);
 			break;
 		case BPF_STX | BPF_ATOMIC | BPF_DW:
-			if (insn->imm != BPF_ADD) {
+			if (imm != BPF_ADD) {
 				pr_err_ratelimited(
 					"eBPF filter atomic op code %02x (@%d) unsupported\n",
 					code, i);