linux-kernel - Re: [PATCH v7 3/7] mseal, system mappings: enable x86-64

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Message-ID: <CABi2SkUwETzrBSYm0QV9+eoeo0kgA+r2JM4QaFpQqeTiidFEDA@mail.gmail.com>
Date: Tue, 25 Feb 2025 16:48:47 -0800
From: Jeff Xu <jeffxu@...omium.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: akpm@...ux-foundation.org, keescook@...omium.org, jannh@...gle.com, 
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Subject: Re: [PATCH v7 3/7] mseal, system mappings: enable x86-64

On Tue, Feb 25, 2025 at 12:08 AM Thomas Weißschuh
<thomas.weissschuh@...utronix.de> wrote:
>
> Hi Jeff,
>
> On Mon, Feb 24, 2025 at 10:52:42PM +0000, jeffxu@...omium.org wrote:
> > From: Jeff Xu <jeffxu@...omium.org>
> >
> > Provide support for CONFIG_MSEAL_SYSTEM_MAPPINGS on x86-64,
> > covering the vdso, vvar, vvar_vclock.
> >
> > Production release testing passes on Android and Chrome OS.
> >
> > Signed-off-by: Jeff Xu <jeffxu@...omium.org>
> > ---
> >  arch/x86/Kconfig          |  1 +
> >  arch/x86/entry/vdso/vma.c | 16 ++++++++++------
> >  2 files changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 87198d957e2f..8fa17032ca46 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -26,6 +26,7 @@ config X86_64
> >       depends on 64BIT
> >       # Options that are inherently 64-bit kernel only:
> >       select ARCH_HAS_GIGANTIC_PAGE
> > +     select ARCH_HAS_MSEAL_SYSTEM_MAPPINGS
> >       select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
> >       select ARCH_SUPPORTS_PER_VMA_LOCK
> >       select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
> > diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> > index 39e6efc1a9ca..1b1c009f20a8 100644
> > --- a/arch/x86/entry/vdso/vma.c
> > +++ b/arch/x86/entry/vdso/vma.c
> > @@ -247,6 +247,7 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
> >       struct mm_struct *mm = current->mm;
> >       struct vm_area_struct *vma;
> >       unsigned long text_start;
> > +     unsigned long vm_flags;
> >       int ret = 0;
> >
> >       if (mmap_write_lock_killable(mm))
> > @@ -264,11 +265,12 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
> >       /*
> >        * MAYWRITE to allow gdb to COW and set breakpoints
> >        */
> > +     vm_flags = VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC;
> > +     vm_flags |= VM_SEALED_SYSMAP;
> >       vma = _install_special_mapping(mm,
> >                                      text_start,
> >                                      image->size,
> > -                                    VM_READ|VM_EXEC|
> > -                                    VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
> > +                                    vm_flags,
> >                                      &vdso_mapping);
> >
> >       if (IS_ERR(vma)) {
> > @@ -276,11 +278,12 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
> >               goto up_fail;
> >       }
> >
> > +     vm_flags = VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|VM_PFNMAP;
> > +     vm_flags |= VM_SEALED_SYSMAP;
> >       vma = _install_special_mapping(mm,
> >                                      addr,
> >                                      (__VVAR_PAGES - VDSO_NR_VCLOCK_PAGES) * PAGE_SIZE,
> > -                                    VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
> > -                                    VM_PFNMAP,
> > +                                    vm_flags,
> >                                      &vvar_mapping);
>
> This hunk (and the vvar mapping in the arm64 patch) will conflict with my
> "Generic vDSO datapage" series.
> That series is already part of the tip tree (branch timers/vdso) and scheduled
> for the next merge window.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=timers/vdso
>
> The conflict resolution is fairly easy:
> Move the new flag logic into lib/vdso/datastore.c
>
Thank you for bringing this to my attention.

In your change,  it seems lib/vdso/datastore.c implements a
vdso_install_vvar_mapping(), then all the architectures call this
function.

So merging conflict won't be as straightforward.  Maybe a better
approach is that I continue resolving all the comments, based on the
latest main. Then wait for your change to be merged and submit another
version.

Thanks
-Jeff

-Jeff