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[PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0

Tiezhu Yang posted 1 patch 1 month ago 
arch/loongarch/net/bpf_jit.c | 5 +++++
1 file changed, 5 insertions(+)
[PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0
Posted by Tiezhu Yang 1 month ago 
Occasionally, there exists "text_copy_cb: operation failed" when executing
bpf selftests, the reason is copy_to_kernel_nofault() failed and the ecode
of estat register is 0x4 (PME: Page Modification Exception) due to the pte
is not writeable, the root cause is that there is another place to set pte
readonly which is in the generic weak arch_protect_bpf_trampoline().

There are two ways to fix this race condition issue, the direct way is to
modify the generic weak arch_protect_bpf_trampoline() to add a mutex lock
for set_memory_rox(), but the other simple and proper way is to just make
arch_protect_bpf_trampoline() return 0 in the arch-specific code because
LoongArch already uses BPF prog pack allocator for trampoline.

Here are the trimmed kernel log messages:

  copy_to_kernel_nofault: memory access failed, ecode is 0x4
  copy_to_kernel_nofault: caller is text_copy_cb+0x50/0xa0
  text_copy_cb: operation failed
  ------------[ cut here ]------------
  bpf_prog_pack bug: missing bpf_arch_text_invalidate?
  WARNING: kernel/bpf/core.c:1008 at bpf_prog_pack_free+0x200/0x228
  ...
  Call Trace:
  [<9000000000248914>] show_stack+0x64/0x188
  [<9000000000241308>] dump_stack_lvl+0x6c/0x9c
  [<90000000002705bc>] __warn+0x9c/0x200
  [<9000000001c428c0>] __report_bug+0xa8/0x1c0
  [<9000000001c42b5c>] report_bug+0x64/0x120
  [<9000000001c7dcd0>] do_bp+0x270/0x3c0
  [<9000000000246f40>] handle_bp+0x120/0x1c0
  [<900000000047b030>] bpf_prog_pack_free+0x200/0x228
  [<900000000047b2ec>] bpf_jit_binary_pack_free+0x24/0x60
  [<900000000026989c>] bpf_jit_free+0x54/0xb0
  [<900000000029e10c>] process_one_work+0x184/0x610
  [<900000000029ef8c>] worker_thread+0x24c/0x388
  [<90000000002a902c>] kthread+0x13c/0x170
  [<9000000001c7dfe8>] ret_from_kernel_thread+0x28/0x1c0
  [<9000000000246624>] ret_from_kernel_thread_asm+0xc/0x88

  ---[ end trace 0000000000000000 ]---

Here is a simple shell script to reproduce:

  #!/bin/bash

  for ((i=1; i<=1000; i++))
  do
    echo "under testing $i ..."
    dmesg -c > /dev/null
    ./test_progs -t fentry_attach_stress > /dev/null
    dmesg -t | grep "text_copy_cb: operation failed"
    if [ $? -eq 0 ]; then
      break
    fi
  done

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 arch/loongarch/net/bpf_jit.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 3bd89f55960d..4f1af3b7a363 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1568,6 +1568,11 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
 	bpf_prog_pack_free(image, size);
 }
 
+int arch_protect_bpf_trampoline(void *image, unsigned int size)
+{
+	return 0;
+}
+
 /*
  * Sign-extend the register if necessary
  */
-- 
2.42.0
Re: [PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0
Posted by Hengqi Chen 3 weeks, 4 days ago 
On Tue, Mar 10, 2026 at 2:47 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> Occasionally, there exists "text_copy_cb: operation failed" when executing
> bpf selftests, the reason is copy_to_kernel_nofault() failed and the ecode
> of estat register is 0x4 (PME: Page Modification Exception) due to the pte
> is not writeable, the root cause is that there is another place to set pte
> readonly which is in the generic weak arch_protect_bpf_trampoline().
>
> There are two ways to fix this race condition issue, the direct way is to
> modify the generic weak arch_protect_bpf_trampoline() to add a mutex lock
> for set_memory_rox(), but the other simple and proper way is to just make
> arch_protect_bpf_trampoline() return 0 in the arch-specific code because
> LoongArch already uses BPF prog pack allocator for trampoline.
>
> Here are the trimmed kernel log messages:
>
>   copy_to_kernel_nofault: memory access failed, ecode is 0x4
>   copy_to_kernel_nofault: caller is text_copy_cb+0x50/0xa0
>   text_copy_cb: operation failed
>   ------------[ cut here ]------------
>   bpf_prog_pack bug: missing bpf_arch_text_invalidate?
>   WARNING: kernel/bpf/core.c:1008 at bpf_prog_pack_free+0x200/0x228
>   ...
>   Call Trace:
>   [<9000000000248914>] show_stack+0x64/0x188
>   [<9000000000241308>] dump_stack_lvl+0x6c/0x9c
>   [<90000000002705bc>] __warn+0x9c/0x200
>   [<9000000001c428c0>] __report_bug+0xa8/0x1c0
>   [<9000000001c42b5c>] report_bug+0x64/0x120
>   [<9000000001c7dcd0>] do_bp+0x270/0x3c0
>   [<9000000000246f40>] handle_bp+0x120/0x1c0
>   [<900000000047b030>] bpf_prog_pack_free+0x200/0x228
>   [<900000000047b2ec>] bpf_jit_binary_pack_free+0x24/0x60
>   [<900000000026989c>] bpf_jit_free+0x54/0xb0
>   [<900000000029e10c>] process_one_work+0x184/0x610
>   [<900000000029ef8c>] worker_thread+0x24c/0x388
>   [<90000000002a902c>] kthread+0x13c/0x170
>   [<9000000001c7dfe8>] ret_from_kernel_thread+0x28/0x1c0
>   [<9000000000246624>] ret_from_kernel_thread_asm+0xc/0x88
>
>   ---[ end trace 0000000000000000 ]---
>
> Here is a simple shell script to reproduce:
>
>   #!/bin/bash
>
>   for ((i=1; i<=1000; i++))
>   do
>     echo "under testing $i ..."
>     dmesg -c > /dev/null
>     ./test_progs -t fentry_attach_stress > /dev/null
>     dmesg -t | grep "text_copy_cb: operation failed"
>     if [ $? -eq 0 ]; then
>       break
>     fi
>   done
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---

Acked-by: Hengqi Chen <hengqi.chen@gmail.com>

>  arch/loongarch/net/bpf_jit.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 3bd89f55960d..4f1af3b7a363 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -1568,6 +1568,11 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
>         bpf_prog_pack_free(image, size);
>  }
>
> +int arch_protect_bpf_trampoline(void *image, unsigned int size)
> +{
> +       return 0;
> +}
> +
>  /*
>   * Sign-extend the register if necessary
>   */
> --
> 2.42.0
>
Re: [PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0
Posted by Huacai Chen 3 weeks, 3 days ago 
Applied, thanks.

Huacai

On Sun, Mar 15, 2026 at 11:27 AM Hengqi Chen <hengqi.chen@gmail.com> wrote:
>
> On Tue, Mar 10, 2026 at 2:47 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
> >
> > Occasionally, there exists "text_copy_cb: operation failed" when executing
> > bpf selftests, the reason is copy_to_kernel_nofault() failed and the ecode
> > of estat register is 0x4 (PME: Page Modification Exception) due to the pte
> > is not writeable, the root cause is that there is another place to set pte
> > readonly which is in the generic weak arch_protect_bpf_trampoline().
> >
> > There are two ways to fix this race condition issue, the direct way is to
> > modify the generic weak arch_protect_bpf_trampoline() to add a mutex lock
> > for set_memory_rox(), but the other simple and proper way is to just make
> > arch_protect_bpf_trampoline() return 0 in the arch-specific code because
> > LoongArch already uses BPF prog pack allocator for trampoline.
> >
> > Here are the trimmed kernel log messages:
> >
> >   copy_to_kernel_nofault: memory access failed, ecode is 0x4
> >   copy_to_kernel_nofault: caller is text_copy_cb+0x50/0xa0
> >   text_copy_cb: operation failed
> >   ------------[ cut here ]------------
> >   bpf_prog_pack bug: missing bpf_arch_text_invalidate?
> >   WARNING: kernel/bpf/core.c:1008 at bpf_prog_pack_free+0x200/0x228
> >   ...
> >   Call Trace:
> >   [<9000000000248914>] show_stack+0x64/0x188
> >   [<9000000000241308>] dump_stack_lvl+0x6c/0x9c
> >   [<90000000002705bc>] __warn+0x9c/0x200
> >   [<9000000001c428c0>] __report_bug+0xa8/0x1c0
> >   [<9000000001c42b5c>] report_bug+0x64/0x120
> >   [<9000000001c7dcd0>] do_bp+0x270/0x3c0
> >   [<9000000000246f40>] handle_bp+0x120/0x1c0
> >   [<900000000047b030>] bpf_prog_pack_free+0x200/0x228
> >   [<900000000047b2ec>] bpf_jit_binary_pack_free+0x24/0x60
> >   [<900000000026989c>] bpf_jit_free+0x54/0xb0
> >   [<900000000029e10c>] process_one_work+0x184/0x610
> >   [<900000000029ef8c>] worker_thread+0x24c/0x388
> >   [<90000000002a902c>] kthread+0x13c/0x170
> >   [<9000000001c7dfe8>] ret_from_kernel_thread+0x28/0x1c0
> >   [<9000000000246624>] ret_from_kernel_thread_asm+0xc/0x88
> >
> >   ---[ end trace 0000000000000000 ]---
> >
> > Here is a simple shell script to reproduce:
> >
> >   #!/bin/bash
> >
> >   for ((i=1; i<=1000; i++))
> >   do
> >     echo "under testing $i ..."
> >     dmesg -c > /dev/null
> >     ./test_progs -t fentry_attach_stress > /dev/null
> >     dmesg -t | grep "text_copy_cb: operation failed"
> >     if [ $? -eq 0 ]; then
> >       break
> >     fi
> >   done
> >
> > Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> > ---
>
> Acked-by: Hengqi Chen <hengqi.chen@gmail.com>
>
> >  arch/loongarch/net/bpf_jit.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> > index 3bd89f55960d..4f1af3b7a363 100644
> > --- a/arch/loongarch/net/bpf_jit.c
> > +++ b/arch/loongarch/net/bpf_jit.c
> > @@ -1568,6 +1568,11 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
> >         bpf_prog_pack_free(image, size);
> >  }
> >
> > +int arch_protect_bpf_trampoline(void *image, unsigned int size)
> > +{
> > +       return 0;
> > +}
> > +
> >  /*
> >   * Sign-extend the register if necessary
> >   */
> > --
> > 2.42.0
> >
Re: [PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0
Posted by bot+bpf-ci@kernel.org 4 weeks, 1 day ago 
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 3bd89f55960d..4f1af3b7a363 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -1568,6 +1568,11 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
>  	bpf_prog_pack_free(image, size);
>  }
>
> +int arch_protect_bpf_trampoline(void *image, unsigned int size)
> +{
> +	return 0;
> +}

The fix itself looks correct and is consistent with x86, arm64, and
powerpc which all override arch_protect_bpf_trampoline() to return 0
when using the prog pack allocator.

Should this have a Fixes: tag? The race was introduced when LoongArch
switched to the prog pack allocator without overriding the protect
function. Consider adding:

Fixes: 4ab17e762b34 ("LoongArch: BPF: Use BPF prog pack allocator")

---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/22891104109

Patchew 2.1-devel-ea86937

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