* [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly
@ 2025-09-04 10:38 Hengqi Chen
2025-09-04 22:42 ` Amery Hung
2025-09-05 2:15 ` Pu Lehui
0 siblings, 2 replies; 5+ messages in thread
From: Hengqi Chen @ 2025-09-04 10:38 UTC (permalink / raw)
To: ast, daniel, andrii, martin.lau, bjorn, pulehui, puranjay
Cc: bpf, linux-riscv, Hengqi Chen
The ns_bpf_qdisc selftest triggers a kernel panic:
Unable to handle kernel paging request at virtual address ffffffffa38dbf58
Current test_progs pgtable: 4K pagesize, 57-bit VAs, pgdp=0x00000001109cc000
[ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401, pud=000000011fffd001, pmd=0000000000000000
Oops [#1]
Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1 dm_mod drm drm_panel_orientation_quirks configfs backlight btrfs blake2b_generic xor lzo_compress zlib_deflate raid6_pq efivarfs [last unloaded: bpf_testmod(OE)]
CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G W OE 6.17.0-rc1-g2465bb83e0b4 #1 NONE
Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01+dfsg-1ubuntu5.1 01/01/2024
epc : __qdisc_run+0x82/0x6f0
ra : __qdisc_run+0x6e/0x6f0
epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
t5 : 0000000000000000 t6 : ff60000093a6a8b6
status: 0000000200000120 badaddr: ffffffffa38dbf58 cause: 000000000000000d
[<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
[<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
[<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
[<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
[<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
[<ffffffff80d31446>] ip6_output+0x5e/0x178
[<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
[<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
[<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
[<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
[<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
[<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
[<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
[<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
[<ffffffff80b42bee>] __sys_connect+0x96/0xc8
[<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
[<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
[<ffffffff80e69af2>] handle_exception+0x14a/0x156
Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
---[ end trace 0000000000000000 ]---
The bpf_fifo_dequeue prog returns a skb which is a pointer.
The pointer is treated as a 32bit value and sign extend to
64bit in epilogue. This behavior is right for most bpf prog
types but wrong for struct ops which requires RISC-V ABI.
So let's sign extend struct ops return values according to
the function model and RISC-V ABI([0]).
[0]: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf
Fixes: 25ad10658dc1 ("riscv, bpf: Adapt bpf trampoline to optimized riscv ftrace framework")
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
arch/riscv/net/bpf_jit_comp64.c | 38 ++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 549c3063c7f1..c7ae4d0a8361 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -954,6 +954,35 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
return ret;
}
+/*
+ * Sign-extend the register if necessary
+ */
+static int sign_extend(int rd, int rs, u8 size, u8 flags, struct rv_jit_context *ctx)
+{
+ if (!(flags & BTF_FMODEL_SIGNED_ARG) && (size == 1 || size == 2))
+ return 0;
+
+ switch (size) {
+ case 1:
+ emit_sextb(rd, rs, ctx);
+ break;
+ case 2:
+ emit_sexth(rd, rs, ctx);
+ break;
+ case 4:
+ emit_sextw(rd, rs, ctx);
+ break;
+ case 8:
+ emit_mv(rd, rs, ctx);
+ break;
+ default:
+ pr_err("bpf-jit: invalid size %d for sign_extend\n", size);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
const struct btf_func_model *m,
struct bpf_tramp_links *tlinks,
@@ -1175,8 +1204,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
if (save_ret) {
- emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
emit_ld(regmap[BPF_REG_0], -(retval_off - 8), RV_REG_FP, ctx);
+ if (is_struct_ops) {
+ ret = sign_extend(RV_REG_A0, regmap[BPF_REG_0],
+ m->ret_size, m->ret_flags, ctx);
+ if (ret)
+ goto out;
+ } else {
+ emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
+ }
}
emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
--
2.45.2
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^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly
2025-09-04 10:38 [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly Hengqi Chen
@ 2025-09-04 22:42 ` Amery Hung
2025-09-05 1:24 ` Hengqi Chen
2025-09-05 2:15 ` Pu Lehui
1 sibling, 1 reply; 5+ messages in thread
From: Amery Hung @ 2025-09-04 22:42 UTC (permalink / raw)
To: Hengqi Chen, ast, daniel, andrii, martin.lau, bjorn, pulehui,
puranjay
Cc: bpf, linux-riscv
On 9/4/25 3:38 AM, Hengqi Chen wrote:
> The ns_bpf_qdisc selftest triggers a kernel panic:
>
> Unable to handle kernel paging request at virtual address ffffffffa38dbf58
> Current test_progs pgtable: 4K pagesize, 57-bit VAs, pgdp=0x00000001109cc000
> [ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401, pud=000000011fffd001, pmd=0000000000000000
> Oops [#1]
> Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1 dm_mod drm drm_panel_orientation_quirks configfs backlight btrfs blake2b_generic xor lzo_compress zlib_deflate raid6_pq efivarfs [last unloaded: bpf_testmod(OE)]
> CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G W OE 6.17.0-rc1-g2465bb83e0b4 #1 NONE
> Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
> Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01+dfsg-1ubuntu5.1 01/01/2024
> epc : __qdisc_run+0x82/0x6f0
> ra : __qdisc_run+0x6e/0x6f0
> epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
> gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
> t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
> s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
> a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
> a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
> s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
> s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
> s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
> s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
> t5 : 0000000000000000 t6 : ff60000093a6a8b6
> status: 0000000200000120 badaddr: ffffffffa38dbf58 cause: 000000000000000d
> [<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
> [<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
> [<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
> [<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
> [<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
> [<ffffffff80d31446>] ip6_output+0x5e/0x178
> [<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
> [<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
> [<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
> [<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
> [<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
> [<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
> [<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
> [<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
> [<ffffffff80b42bee>] __sys_connect+0x96/0xc8
> [<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
> [<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
> [<ffffffff80e69af2>] handle_exception+0x14a/0x156
> Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
> ---[ end trace 0000000000000000 ]---
>
> The bpf_fifo_dequeue prog returns a skb which is a pointer.
> The pointer is treated as a 32bit value and sign extend to
> 64bit in epilogue. This behavior is right for most bpf prog
> types but wrong for struct ops which requires RISC-V ABI.
>
> So let's sign extend struct ops return values according to
> the function model and RISC-V ABI([0]).
>
> [0]: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf
>
> Fixes: 25ad10658dc1 ("riscv, bpf: Adapt bpf trampoline to optimized riscv ftrace framework")
> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> ---
> arch/riscv/net/bpf_jit_comp64.c | 38 ++++++++++++++++++++++++++++++++-
> 1 file changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 549c3063c7f1..c7ae4d0a8361 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -954,6 +954,35 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
> return ret;
> }
>
> +/*
> + * Sign-extend the register if necessary
> + */
> +static int sign_extend(int rd, int rs, u8 size, u8 flags, struct rv_jit_context *ctx)
> +{
> + if (!(flags & BTF_FMODEL_SIGNED_ARG) && (size == 1 || size == 2))
> + return 0;
> +
> + switch (size) {
> + case 1:
> + emit_sextb(rd, rs, ctx);
> + break;
> + case 2:
> + emit_sexth(rd, rs, ctx);
> + break;
> + case 4:
> + emit_sextw(rd, rs, ctx);
> + break;
> + case 8:
> + emit_mv(rd, rs, ctx);
> + break;
> + default:
> + pr_err("bpf-jit: invalid size %d for sign_extend\n", size);
> + return -EINVAL;
Will this accidentally rejects struct_ops functions that return void?
> + }
> +
> + return 0;
> +}
> +
> static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> const struct btf_func_model *m,
> struct bpf_tramp_links *tlinks,
> @@ -1175,8 +1204,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
>
> if (save_ret) {
> - emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> emit_ld(regmap[BPF_REG_0], -(retval_off - 8), RV_REG_FP, ctx);
> + if (is_struct_ops) {
> + ret = sign_extend(RV_REG_A0, regmap[BPF_REG_0],
> + m->ret_size, m->ret_flags, ctx);
> + if (ret)
> + goto out;
> + } else {
> + emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> + }
> }
>
> emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
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http://lists.infradead.org/mailman/listinfo/linux-riscv
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly
2025-09-04 22:42 ` Amery Hung
@ 2025-09-05 1:24 ` Hengqi Chen
2025-09-08 22:34 ` Amery Hung
0 siblings, 1 reply; 5+ messages in thread
From: Hengqi Chen @ 2025-09-05 1:24 UTC (permalink / raw)
To: Amery Hung
Cc: ast, daniel, andrii, martin.lau, bjorn, pulehui, puranjay, bpf,
linux-riscv
On Fri, Sep 5, 2025 at 6:42 AM Amery Hung <ameryhung@gmail.com> wrote:
>
>
>
> On 9/4/25 3:38 AM, Hengqi Chen wrote:
> > The ns_bpf_qdisc selftest triggers a kernel panic:
> >
> > Unable to handle kernel paging request at virtual address ffffffffa38dbf58
> > Current test_progs pgtable: 4K pagesize, 57-bit VAs, pgdp=0x00000001109cc000
> > [ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401, pud=000000011fffd001, pmd=0000000000000000
> > Oops [#1]
> > Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1 dm_mod drm drm_panel_orientation_quirks configfs backlight btrfs blake2b_generic xor lzo_compress zlib_deflate raid6_pq efivarfs [last unloaded: bpf_testmod(OE)]
> > CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G W OE 6.17.0-rc1-g2465bb83e0b4 #1 NONE
> > Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
> > Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01+dfsg-1ubuntu5.1 01/01/2024
> > epc : __qdisc_run+0x82/0x6f0
> > ra : __qdisc_run+0x6e/0x6f0
> > epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
> > gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
> > t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
> > s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
> > a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
> > a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
> > s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
> > s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
> > s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
> > s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
> > t5 : 0000000000000000 t6 : ff60000093a6a8b6
> > status: 0000000200000120 badaddr: ffffffffa38dbf58 cause: 000000000000000d
> > [<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
> > [<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
> > [<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
> > [<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
> > [<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
> > [<ffffffff80d31446>] ip6_output+0x5e/0x178
> > [<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
> > [<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
> > [<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
> > [<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
> > [<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
> > [<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
> > [<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
> > [<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
> > [<ffffffff80b42bee>] __sys_connect+0x96/0xc8
> > [<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
> > [<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
> > [<ffffffff80e69af2>] handle_exception+0x14a/0x156
> > Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
> > ---[ end trace 0000000000000000 ]---
> >
> > The bpf_fifo_dequeue prog returns a skb which is a pointer.
> > The pointer is treated as a 32bit value and sign extend to
> > 64bit in epilogue. This behavior is right for most bpf prog
> > types but wrong for struct ops which requires RISC-V ABI.
> >
> > So let's sign extend struct ops return values according to
> > the function model and RISC-V ABI([0]).
> >
> > [0]: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf
> >
> > Fixes: 25ad10658dc1 ("riscv, bpf: Adapt bpf trampoline to optimized riscv ftrace framework")
> > Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> > ---
> > arch/riscv/net/bpf_jit_comp64.c | 38 ++++++++++++++++++++++++++++++++-
> > 1 file changed, 37 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> > index 549c3063c7f1..c7ae4d0a8361 100644
> > --- a/arch/riscv/net/bpf_jit_comp64.c
> > +++ b/arch/riscv/net/bpf_jit_comp64.c
> > @@ -954,6 +954,35 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
> > return ret;
> > }
> >
> > +/*
> > + * Sign-extend the register if necessary
> > + */
> > +static int sign_extend(int rd, int rs, u8 size, u8 flags, struct rv_jit_context *ctx)
> > +{
> > + if (!(flags & BTF_FMODEL_SIGNED_ARG) && (size == 1 || size == 2))
> > + return 0;
> > +
> > + switch (size) {
> > + case 1:
> > + emit_sextb(rd, rs, ctx);
> > + break;
> > + case 2:
> > + emit_sexth(rd, rs, ctx);
> > + break;
> > + case 4:
> > + emit_sextw(rd, rs, ctx);
> > + break;
> > + case 8:
> > + emit_mv(rd, rs, ctx);
> > + break;
> > + default:
> > + pr_err("bpf-jit: invalid size %d for sign_extend\n", size);
> > + return -EINVAL;
>
> Will this accidentally rejects struct_ops functions that return void?
>
No, see https://elixir.bootlin.com/linux/v6.16.4/source/kernel/bpf/bpf_struct_ops.c#L601-L602
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> > const struct btf_func_model *m,
> > struct bpf_tramp_links *tlinks,
> > @@ -1175,8 +1204,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> > restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
> >
> > if (save_ret) {
> > - emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> > emit_ld(regmap[BPF_REG_0], -(retval_off - 8), RV_REG_FP, ctx);
> > + if (is_struct_ops) {
> > + ret = sign_extend(RV_REG_A0, regmap[BPF_REG_0],
> > + m->ret_size, m->ret_flags, ctx);
> > + if (ret)
> > + goto out;
> > + } else {
> > + emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> > + }
> > }
> >
> > emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
>
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly
2025-09-04 10:38 [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly Hengqi Chen
2025-09-04 22:42 ` Amery Hung
@ 2025-09-05 2:15 ` Pu Lehui
1 sibling, 0 replies; 5+ messages in thread
From: Pu Lehui @ 2025-09-05 2:15 UTC (permalink / raw)
To: Hengqi Chen, ast, daniel, andrii, martin.lau, bjorn, puranjay
Cc: bpf, linux-riscv
On 2025/9/4 18:38, Hengqi Chen wrote:
> The ns_bpf_qdisc selftest triggers a kernel panic:
>
> Unable to handle kernel paging request at virtual address ffffffffa38dbf58
> Current test_progs pgtable: 4K pagesize, 57-bit VAs, pgdp=0x00000001109cc000
> [ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401, pud=000000011fffd001, pmd=0000000000000000
> Oops [#1]
> Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1 dm_mod drm drm_panel_orientation_quirks configfs backlight btrfs blake2b_generic xor lzo_compress zlib_deflate raid6_pq efivarfs [last unloaded: bpf_testmod(OE)]
> CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G W OE 6.17.0-rc1-g2465bb83e0b4 #1 NONE
> Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
> Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01+dfsg-1ubuntu5.1 01/01/2024
> epc : __qdisc_run+0x82/0x6f0
> ra : __qdisc_run+0x6e/0x6f0
> epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
> gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
> t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
> s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
> a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
> a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
> s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
> s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
> s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
> s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
> t5 : 0000000000000000 t6 : ff60000093a6a8b6
> status: 0000000200000120 badaddr: ffffffffa38dbf58 cause: 000000000000000d
> [<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
> [<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
> [<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
> [<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
> [<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
> [<ffffffff80d31446>] ip6_output+0x5e/0x178
> [<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
> [<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
> [<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
> [<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
> [<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
> [<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
> [<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
> [<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
> [<ffffffff80b42bee>] __sys_connect+0x96/0xc8
> [<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
> [<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
> [<ffffffff80e69af2>] handle_exception+0x14a/0x156
> Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
> ---[ end trace 0000000000000000 ]---
>
> The bpf_fifo_dequeue prog returns a skb which is a pointer.
> The pointer is treated as a 32bit value and sign extend to
> 64bit in epilogue. This behavior is right for most bpf prog
> types but wrong for struct ops which requires RISC-V ABI.
>
> So let's sign extend struct ops return values according to
> the function model and RISC-V ABI([0]).
>
> [0]: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf
>
> Fixes: 25ad10658dc1 ("riscv, bpf: Adapt bpf trampoline to optimized riscv ftrace framework")
> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> ---
> arch/riscv/net/bpf_jit_comp64.c | 38 ++++++++++++++++++++++++++++++++-
> 1 file changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 549c3063c7f1..c7ae4d0a8361 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -954,6 +954,35 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
> return ret;
> }
>
> +/*
> + * Sign-extend the register if necessary
> + */
This helper may be used later, so let's put it higher.
> +static int sign_extend(int rd, int rs, u8 size, u8 flags, struct rv_jit_context *ctx)
> +{
> + if (!(flags & BTF_FMODEL_SIGNED_ARG) && (size == 1 || size == 2))
emm, this will miss unsigned 1 and 2 byte return values, we should also
move them to RV_REG_A0. And also, let we use `sign` but not `flags`, as
we may use this helper in other place. That will be:
static int sign_extend(u8 rd, u8 rs, u8 sz, bool sign, struct
rv_jit_context *ctx)
{
if (!sign && (sz == 1 || sz == 2)) {
if (rd != rs)
emit_mv(rd, rs, ctx);
return 0;
}
...
}
> + return 0;
> +
> + switch (size) {
> + case 1:
> + emit_sextb(rd, rs, ctx);
> + break;
> + case 2:
> + emit_sexth(rd, rs, ctx);
> + break;
> + case 4:
> + emit_sextw(rd, rs, ctx);
> + break;
> + case 8:
let's only move when rd != rs
> + emit_mv(rd, rs, ctx);
> + break;
> + default:
> + pr_err("bpf-jit: invalid size %d for sign_extend\n", size);
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +
> static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> const struct btf_func_model *m,
> struct bpf_tramp_links *tlinks,
> @@ -1175,8 +1204,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
>
> if (save_ret) {
> - emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> emit_ld(regmap[BPF_REG_0], -(retval_off - 8), RV_REG_FP, ctx);
> + if (is_struct_ops) {
> + ret = sign_extend(RV_REG_A0, regmap[BPF_REG_0],
> + m->ret_size, m->ret_flags, ctx);
> + if (ret)
> + goto out;
> + } else {
> + emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> + }
> }
>
> emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly
2025-09-05 1:24 ` Hengqi Chen
@ 2025-09-08 22:34 ` Amery Hung
0 siblings, 0 replies; 5+ messages in thread
From: Amery Hung @ 2025-09-08 22:34 UTC (permalink / raw)
To: Hengqi Chen
Cc: ast, daniel, andrii, martin.lau, bjorn, pulehui, puranjay, bpf,
linux-riscv
On Thu, Sep 4, 2025 at 6:24 PM Hengqi Chen <hengqi.chen@gmail.com> wrote:
>
> On Fri, Sep 5, 2025 at 6:42 AM Amery Hung <ameryhung@gmail.com> wrote:
> >
> >
> >
> > On 9/4/25 3:38 AM, Hengqi Chen wrote:
> > > The ns_bpf_qdisc selftest triggers a kernel panic:
> > >
> > > Unable to handle kernel paging request at virtual address ffffffffa38dbf58
> > > Current test_progs pgtable: 4K pagesize, 57-bit VAs, pgdp=0x00000001109cc000
> > > [ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401, pud=000000011fffd001, pmd=0000000000000000
> > > Oops [#1]
> > > Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1 dm_mod drm drm_panel_orientation_quirks configfs backlight btrfs blake2b_generic xor lzo_compress zlib_deflate raid6_pq efivarfs [last unloaded: bpf_testmod(OE)]
> > > CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G W OE 6.17.0-rc1-g2465bb83e0b4 #1 NONE
> > > Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
> > > Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01+dfsg-1ubuntu5.1 01/01/2024
> > > epc : __qdisc_run+0x82/0x6f0
> > > ra : __qdisc_run+0x6e/0x6f0
> > > epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
> > > gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
> > > t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
> > > s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
> > > a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
> > > a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
> > > s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
> > > s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
> > > s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
> > > s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
> > > t5 : 0000000000000000 t6 : ff60000093a6a8b6
> > > status: 0000000200000120 badaddr: ffffffffa38dbf58 cause: 000000000000000d
> > > [<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
> > > [<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
> > > [<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
> > > [<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
> > > [<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
> > > [<ffffffff80d31446>] ip6_output+0x5e/0x178
> > > [<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
> > > [<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
> > > [<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
> > > [<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
> > > [<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
> > > [<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
> > > [<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
> > > [<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
> > > [<ffffffff80b42bee>] __sys_connect+0x96/0xc8
> > > [<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
> > > [<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
> > > [<ffffffff80e69af2>] handle_exception+0x14a/0x156
> > > Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
> > > ---[ end trace 0000000000000000 ]---
> > >
> > > The bpf_fifo_dequeue prog returns a skb which is a pointer.
> > > The pointer is treated as a 32bit value and sign extend to
> > > 64bit in epilogue. This behavior is right for most bpf prog
> > > types but wrong for struct ops which requires RISC-V ABI.
> > >
> > > So let's sign extend struct ops return values according to
> > > the function model and RISC-V ABI([0]).
> > >
> > > [0]: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf
> > >
> > > Fixes: 25ad10658dc1 ("riscv, bpf: Adapt bpf trampoline to optimized riscv ftrace framework")
> > > Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> > > ---
> > > arch/riscv/net/bpf_jit_comp64.c | 38 ++++++++++++++++++++++++++++++++-
> > > 1 file changed, 37 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> > > index 549c3063c7f1..c7ae4d0a8361 100644
> > > --- a/arch/riscv/net/bpf_jit_comp64.c
> > > +++ b/arch/riscv/net/bpf_jit_comp64.c
> > > @@ -954,6 +954,35 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
> > > return ret;
> > > }
> > >
> > > +/*
> > > + * Sign-extend the register if necessary
> > > + */
> > > +static int sign_extend(int rd, int rs, u8 size, u8 flags, struct rv_jit_context *ctx)
> > > +{
> > > + if (!(flags & BTF_FMODEL_SIGNED_ARG) && (size == 1 || size == 2))
> > > + return 0;
> > > +
> > > + switch (size) {
> > > + case 1:
> > > + emit_sextb(rd, rs, ctx);
> > > + break;
> > > + case 2:
> > > + emit_sexth(rd, rs, ctx);
> > > + break;
> > > + case 4:
> > > + emit_sextw(rd, rs, ctx);
> > > + break;
> > > + case 8:
> > > + emit_mv(rd, rs, ctx);
> > > + break;
> > > + default:
> > > + pr_err("bpf-jit: invalid size %d for sign_extend\n", size);
> > > + return -EINVAL;
> >
> > Will this accidentally rejects struct_ops functions that return void?
> >
>
> No, see https://elixir.bootlin.com/linux/v6.16.4/source/kernel/bpf/bpf_struct_ops.c#L601-L602
Ah, I see. Thanks for pointing it out.
>
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> > > const struct btf_func_model *m,
> > > struct bpf_tramp_links *tlinks,
> > > @@ -1175,8 +1204,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> > > restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
> > >
> > > if (save_ret) {
> > > - emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> > > emit_ld(regmap[BPF_REG_0], -(retval_off - 8), RV_REG_FP, ctx);
> > > + if (is_struct_ops) {
> > > + ret = sign_extend(RV_REG_A0, regmap[BPF_REG_0],
> > > + m->ret_size, m->ret_flags, ctx);
> > > + if (ret)
> > > + goto out;
> > > + } else {
> > > + emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> > > + }
> > > }
> > >
> > > emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
> >
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^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2025-09-09 6:52 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2025-09-04 10:38 [PATCH v2 bpf-next] riscv, bpf: Sign extend struct ops return values properly Hengqi Chen
2025-09-04 22:42 ` Amery Hung
2025-09-05 1:24 ` Hengqi Chen
2025-09-08 22:34 ` Amery Hung
2025-09-05 2:15 ` Pu Lehui
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