[PATCH] x86/elf: Fix core dump truncation on CPUs with no extended xfeatures

[PATCH] x86/elf: Fix core dump truncation on CPUs with no extended xfeatures

[yongxin.liu]

From: Yongxin Liu <yongxin.liu@windriver.com>

Zero can be a valid value of num_records. For example, on Intel Atom x6425RE,
only x87 and SSE are supported (features 0, 1), and fpu_user_cfg.max_features
is 3. The for_each_extended_xfeature() loop only iterates feature 2, which is
not enabled, so num_records = 0. This is valid and should not cause core dump
failure.

The size check already validates consistency: if num_records = 0, then
en.n_descsz = 0, so the check passes.

Cc: stable@vger.kernel.org
Fixes: ba386777a30b ("x86/elf: Add a new FPU buffer layout info to x86 core files")
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>
---
 arch/x86/kernel/fpu/xstate.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 48113c5193aa..b1dd30eb21a8 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1984,8 +1984,6 @@ int elf_coredump_extra_notes_write(struct coredump_params *cprm)
 		return 1;
 
 	num_records = dump_xsave_layout_desc(cprm);
-	if (!num_records)
-		return 1;
 
 	/* Total size should be equal to the number of records */
 	if ((sizeof(struct x86_xfeat_component) * num_records) != en.n_descsz)
-- 
2.46.2

Re: [PATCH] x86/elf: Fix core dump truncation on CPUs with no extended xfeatures

[Ingo Molnar]

* yongxin.liu@windriver.com <yongxin.liu@windriver.com> wrote:

> From: Yongxin Liu <yongxin.liu@windriver.com>
>
> Zero can be a valid value of num_records. For example, on Intel Atom x6425RE,
> only x87 and SSE are supported (features 0, 1), and fpu_user_cfg.max_features
> is 3. The for_each_extended_xfeature() loop only iterates feature 2, which is
> not enabled, so num_records = 0. This is valid and should not cause core dump
> failure.
>
> The size check already validates consistency: if num_records = 0, then
> en.n_descsz = 0, so the check passes.
>
> Cc: stable@vger.kernel.org
> Fixes: ba386777a30b ("x86/elf: Add a new FPU buffer layout info to x86 core files")
> Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>
> ---
>  arch/x86/kernel/fpu/xstate.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 48113c5193aa..b1dd30eb21a8 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -1984,8 +1984,6 @@ int elf_coredump_extra_notes_write(struct coredump_params *cprm)
>		return 1;
>
>	num_records = dump_xsave_layout_desc(cprm);
> -	if (!num_records)
> -		return 1;

The problem with your patch is that '0' is also used for other errors,
it's the all-around error flag for core dump helper functions such as
dump_emit():

                if (!dump_emit(cprm, &xc, sizeof(xc)))
                        return 0;

So please change dump_xsave_layout_desc() to use negatives
as genuine errors and otherwise returns num_records, and
change elf_coredump_extra_notes_write() to only abort
on genuine errors.

Thanks,

	Ingo

RE: [PATCH] x86/elf: Fix core dump truncation on CPUs with no extended xfeatures

[Liu, Yongxin]

> -----Original Message-----
> From: Ingo Molnar <mingo@kernel.org>
> Sent: Tuesday, December 9, 2025 17:05
> To: Liu, Yongxin <Yongxin.Liu@windriver.com>
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; bp@alien8.de;
> tglx@linutronix.de; mingo@redhat.com; dave.hansen@linux.intel.com;
> vigbalas@amd.com; stable@vger.kernel.org
> Subject: Re: [PATCH] x86/elf: Fix core dump truncation on CPUs with no
> extended xfeatures
> 
> CAUTION: This email comes from a non Wind River email account!
> Do not click links or open attachments unless you recognize the sender and
> know the content is safe.
> 
> * yongxin.liu@windriver.com <yongxin.liu@windriver.com> wrote:
> 
> > From: Yongxin Liu <yongxin.liu@windriver.com>
> >
> > Zero can be a valid value of num_records. For example, on Intel Atom
> > x6425RE, only x87 and SSE are supported (features 0, 1), and
> > fpu_user_cfg.max_features is 3. The for_each_extended_xfeature() loop
> > only iterates feature 2, which is not enabled, so num_records = 0.
> > This is valid and should not cause core dump failure.
> >
> > The size check already validates consistency: if num_records = 0, then
> > en.n_descsz = 0, so the check passes.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: ba386777a30b ("x86/elf: Add a new FPU buffer layout info to x86
> > core files")
> > Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>
> > ---
> >  arch/x86/kernel/fpu/xstate.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/fpu/xstate.c
> > b/arch/x86/kernel/fpu/xstate.c index 48113c5193aa..b1dd30eb21a8 100644
> > --- a/arch/x86/kernel/fpu/xstate.c
> > +++ b/arch/x86/kernel/fpu/xstate.c
> > @@ -1984,8 +1984,6 @@ int elf_coredump_extra_notes_write(struct
> coredump_params *cprm)
> >               return 1;
> >
> >       num_records = dump_xsave_layout_desc(cprm);
> > -     if (!num_records)
> > -             return 1;
> 
> The problem with your patch is that '0' is also used for other errors,
> it's the all-around error flag for core dump helper functions such as
> dump_emit():
> 
>                 if (!dump_emit(cprm, &xc, sizeof(xc)))
>                         return 0;
> 
> So please change dump_xsave_layout_desc() to use negatives as genuine
> errors and otherwise returns num_records, and change
> elf_coredump_extra_notes_write() to only abort on genuine errors.

Thank you for the review. I'll send a v2 patch addressing your feedback.

Thanks,
Yongxin

> 
> Thanks,
> 
>         Ingo