* [PATCH] s390/bpf: Zero-extend bpf prog return values and kfunc arguments
@ 2026-03-13 17:46 Ilya Leoshkevich
2026-03-16 16:05 ` Ihor Solodrai
2026-03-16 16:30 ` patchwork-bot+netdevbpf
0 siblings, 2 replies; 3+ messages in thread
From: Ilya Leoshkevich @ 2026-03-13 17:46 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko
Cc: bpf, Heiko Carstens, Vasily Gorbik, Alexander Gordeev,
Ilya Leoshkevich, Hari Bathini
s390x ABI requires callers to zero-extend unsigned arguments and
sign-extend signed arguments, and callees to zero-extend unsigned
return values and sign-extend signed return values.
s390 BPF JIT currently implements only sign extension. Fix this
omission and implement zero extension too.
Fixes: 528eb2cb87bc ("s390/bpf: Implement arch_prepare_bpf_trampoline()")
Reported-by: Hari Bathini <hbathini@linux.ibm.com>
Closes: https://lore.kernel.org/bpf/20260312080113.843408-1-hbathini@linux.ibm.com/
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
arch/s390/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------
1 file changed, 24 insertions(+), 15 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 1f9a6b728beb..d08d159b6319 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -830,25 +830,34 @@ static int bpf_jit_probe_post(struct bpf_jit *jit, struct bpf_prog *fp,
}
/*
- * Sign-extend the register if necessary
+ * Sign- or zero-extend the register if necessary
*/
-static int sign_extend(struct bpf_jit *jit, int r, u8 size, u8 flags)
+static int sign_zero_extend(struct bpf_jit *jit, int r, u8 size, u8 flags)
{
- if (!(flags & BTF_FMODEL_SIGNED_ARG))
- return 0;
-
switch (size) {
case 1:
- /* lgbr %r,%r */
- EMIT4(0xb9060000, r, r);
+ if (flags & BTF_FMODEL_SIGNED_ARG)
+ /* lgbr %r,%r */
+ EMIT4(0xb9060000, r, r);
+ else
+ /* llgcr %r,%r */
+ EMIT4(0xb9840000, r, r);
return 0;
case 2:
- /* lghr %r,%r */
- EMIT4(0xb9070000, r, r);
+ if (flags & BTF_FMODEL_SIGNED_ARG)
+ /* lghr %r,%r */
+ EMIT4(0xb9070000, r, r);
+ else
+ /* llghr %r,%r */
+ EMIT4(0xb9850000, r, r);
return 0;
case 4:
- /* lgfr %r,%r */
- EMIT4(0xb9140000, r, r);
+ if (flags & BTF_FMODEL_SIGNED_ARG)
+ /* lgfr %r,%r */
+ EMIT4(0xb9140000, r, r);
+ else
+ /* llgfr %r,%r */
+ EMIT4(0xb9160000, r, r);
return 0;
case 8:
return 0;
@@ -1798,9 +1807,9 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
return -1;
for (j = 0; j < m->nr_args; j++) {
- if (sign_extend(jit, BPF_REG_1 + j,
- m->arg_size[j],
- m->arg_flags[j]))
+ if (sign_zero_extend(jit, BPF_REG_1 + j,
+ m->arg_size[j],
+ m->arg_flags[j]))
return -1;
}
}
@@ -2566,7 +2575,7 @@ static int invoke_bpf_prog(struct bpf_tramp_jit *tjit,
EMIT6_PCREL_RILB_PTR(0xc0050000, REG_14, p->bpf_func);
/* stg %r2,retval_off(%r15) */
if (save_ret) {
- if (sign_extend(jit, REG_2, m->ret_size, m->ret_flags))
+ if (sign_zero_extend(jit, REG_2, m->ret_size, m->ret_flags))
return -1;
EMIT6_DISP_LH(0xe3000000, 0x0024, REG_2, REG_0, REG_15,
tjit->retval_off);
--
2.53.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] s390/bpf: Zero-extend bpf prog return values and kfunc arguments
2026-03-13 17:46 [PATCH] s390/bpf: Zero-extend bpf prog return values and kfunc arguments Ilya Leoshkevich
@ 2026-03-16 16:05 ` Ihor Solodrai
2026-03-16 16:30 ` patchwork-bot+netdevbpf
1 sibling, 0 replies; 3+ messages in thread
From: Ihor Solodrai @ 2026-03-16 16:05 UTC (permalink / raw)
To: Ilya Leoshkevich, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko
Cc: bpf, Heiko Carstens, Vasily Gorbik, Alexander Gordeev,
Hari Bathini
On 3/13/26 10:46 AM, Ilya Leoshkevich wrote:
> s390x ABI requires callers to zero-extend unsigned arguments and
> sign-extend signed arguments, and callees to zero-extend unsigned
> return values and sign-extend signed return values.
>
> s390 BPF JIT currently implements only sign extension. Fix this
> omission and implement zero extension too.
>
> Fixes: 528eb2cb87bc ("s390/bpf: Implement arch_prepare_bpf_trampoline()")
> Reported-by: Hari Bathini <hbathini@linux.ibm.com>
> Closes: https://lore.kernel.org/bpf/20260312080113.843408-1-hbathini@linux.ibm.com/
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
> arch/s390/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++--------------
> 1 file changed, 24 insertions(+), 15 deletions(-)
Hi Ilya,
Tested-by: Ihor Solodrai <ihor.solodrai@linux.dev>
This bug made the BPF CI red. I applied as temporary CI diff.
Interestingly, an AI bot investigated the test failure and came up
with a similar patch [1]. Gotta teach it to scan upstream for existing
fixes first :)
Thank you!
[1] https://github.com/kernel-patches/vmtest/issues/459
>
> diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
> index 1f9a6b728beb..d08d159b6319 100644
> --- a/arch/s390/net/bpf_jit_comp.c
> +++ b/arch/s390/net/bpf_jit_comp.c
> @@ -830,25 +830,34 @@ static int bpf_jit_probe_post(struct bpf_jit *jit, struct bpf_prog *fp,
> }
>
> /*
> - * Sign-extend the register if necessary
> + * Sign- or zero-extend the register if necessary
> */
> -static int sign_extend(struct bpf_jit *jit, int r, u8 size, u8 flags)
> +static int sign_zero_extend(struct bpf_jit *jit, int r, u8 size, u8 flags)
> {
> - if (!(flags & BTF_FMODEL_SIGNED_ARG))
> - return 0;
> -
> switch (size) {
> case 1:
> - /* lgbr %r,%r */
> - EMIT4(0xb9060000, r, r);
> + if (flags & BTF_FMODEL_SIGNED_ARG)
> + /* lgbr %r,%r */
> + EMIT4(0xb9060000, r, r);
> + else
> + /* llgcr %r,%r */
> + EMIT4(0xb9840000, r, r);
> return 0;
> case 2:
> - /* lghr %r,%r */
> - EMIT4(0xb9070000, r, r);
> + if (flags & BTF_FMODEL_SIGNED_ARG)
> + /* lghr %r,%r */
> + EMIT4(0xb9070000, r, r);
> + else
> + /* llghr %r,%r */
> + EMIT4(0xb9850000, r, r);
> return 0;
> case 4:
> - /* lgfr %r,%r */
> - EMIT4(0xb9140000, r, r);
> + if (flags & BTF_FMODEL_SIGNED_ARG)
> + /* lgfr %r,%r */
> + EMIT4(0xb9140000, r, r);
> + else
> + /* llgfr %r,%r */
> + EMIT4(0xb9160000, r, r);
> return 0;
> case 8:
> return 0;
> @@ -1798,9 +1807,9 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
> return -1;
>
> for (j = 0; j < m->nr_args; j++) {
> - if (sign_extend(jit, BPF_REG_1 + j,
> - m->arg_size[j],
> - m->arg_flags[j]))
> + if (sign_zero_extend(jit, BPF_REG_1 + j,
> + m->arg_size[j],
> + m->arg_flags[j]))
> return -1;
> }
> }
> @@ -2566,7 +2575,7 @@ static int invoke_bpf_prog(struct bpf_tramp_jit *tjit,
> EMIT6_PCREL_RILB_PTR(0xc0050000, REG_14, p->bpf_func);
> /* stg %r2,retval_off(%r15) */
> if (save_ret) {
> - if (sign_extend(jit, REG_2, m->ret_size, m->ret_flags))
> + if (sign_zero_extend(jit, REG_2, m->ret_size, m->ret_flags))
> return -1;
> EMIT6_DISP_LH(0xe3000000, 0x0024, REG_2, REG_0, REG_15,
> tjit->retval_off);
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] s390/bpf: Zero-extend bpf prog return values and kfunc arguments
2026-03-13 17:46 [PATCH] s390/bpf: Zero-extend bpf prog return values and kfunc arguments Ilya Leoshkevich
2026-03-16 16:05 ` Ihor Solodrai
@ 2026-03-16 16:30 ` patchwork-bot+netdevbpf
1 sibling, 0 replies; 3+ messages in thread
From: patchwork-bot+netdevbpf @ 2026-03-16 16:30 UTC (permalink / raw)
To: Ilya Leoshkevich; +Cc: ast, daniel, andrii, bpf, hca, gor, agordeev, hbathini
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:
On Fri, 13 Mar 2026 18:46:25 +0100 you wrote:
> s390x ABI requires callers to zero-extend unsigned arguments and
> sign-extend signed arguments, and callees to zero-extend unsigned
> return values and sign-extend signed return values.
>
> s390 BPF JIT currently implements only sign extension. Fix this
> omission and implement zero extension too.
>
> [...]
Here is the summary with links:
- s390/bpf: Zero-extend bpf prog return values and kfunc arguments
https://git.kernel.org/bpf/bpf-next/c/202e42e4aa89
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-03-16 16:05 ` Ihor Solodrai
2026-03-16 16:30 ` patchwork-bot+netdevbpf
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