Hi Thomas
On Tue, Feb 25, 2025 at 11:35 PM Thomas Weißschuh
<thomas.weissschuh@xxxxxxxxxxxxx> wrote:
>
> On Tue, Feb 25, 2025 at 04:48:47PM -0800, Jeff Xu wrote:
> > On Tue, Feb 25, 2025 at 12:08 AM Thomas Weißschuh
> > <thomas.weissschuh@xxxxxxxxxxxxx> wrote:
> > > On Mon, Feb 24, 2025 at 10:52:42PM +0000, jeffxu@xxxxxxxxxxxx wrote:
> > > > From: Jeff Xu <jeffxu@xxxxxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxxxxx>
> > > > ---
> > > > 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.
>
> Correct.
>
> At least all the architectures using the generic vDSO infrastructure,
> which are the ones you care about.
> Sparc for example has its own implementation.
>
> > So merging conflict won't be as straightforward.
>
> Wouldn't it be enough to unconditionally use VM_SEALED_SYSMAP in
> vdso_install_vvar_mapping()?
> The symbol is a noop on architectures or configurations where the new
> functionality is not available or enabled.
>
Yes. That will work.
> > 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.
>
> That would work, too. As you prefer.
Great !
Thanks
-Jeff
