Re: [PATCH v7 5/7] mseal, system mappings: enable uml architecture

["Berg, Benjamin" <benjamin.berg@intel.com>]

Hi,

On Tue, 2025-02-25 at 06:22 +0000, Lorenzo Stoakes wrote:
> On Mon, Feb 24, 2025 at 10:52:44PM +0000, jeffxu@chromium.org wrote:
> > From: Jeff Xu <jeffxu@chromium.org>
> > 
> > Provide support for CONFIG_MSEAL_SYSTEM_MAPPINGS on UML, covering
> > the vdso.
> > 
> > Testing passes on UML.
> 
> Maybe expand on this by stating that it has been confirmed by Benjamin (I
> _believe_) that UML has no need for problematic relocation so this is known to
> be good.

I may well be misreading this message, but this sounds to me that this
is a misinterpretation. So, just to clarify in case that is needed.

CONFIG_MSEAL_SYSTEM_MAPPINGS does work fine for the UML kernel.
However, the UML kernel is a normal userspace application itself and
for this application to run, the host kernel must have the feature
disabled.

So, UML supports the feature. But it still *cannot* run on a host
machine that has the feature enabled.

Benjamin

> 
> > 
> > Signed-off-by: Jeff Xu <jeffxu@chromium.org>
> > Tested-by: Benjamin Berg <benjamin.berg@intel.com>
> 
> Anyway I know UML has at any rate been confirmed to be good to go +
> patch looks
> fine, so:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> 
> > ---
> >  arch/um/Kconfig        | 1 +
> >  arch/x86/um/vdso/vma.c | 6 ++++--
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> > index 18051b1cfce0..eb2d439a5334 100644
> > --- a/arch/um/Kconfig
> > +++ b/arch/um/Kconfig
> > @@ -10,6 +10,7 @@ config UML
> >  	select ARCH_HAS_FORTIFY_SOURCE
> >  	select ARCH_HAS_GCOV_PROFILE_ALL
> >  	select ARCH_HAS_KCOV
> > +	select ARCH_HAS_MSEAL_SYSTEM_MAPPINGS
> >  	select ARCH_HAS_STRNCPY_FROM_USER
> >  	select ARCH_HAS_STRNLEN_USER
> >  	select HAVE_ARCH_AUDITSYSCALL
> > diff --git a/arch/x86/um/vdso/vma.c b/arch/x86/um/vdso/vma.c
> > index f238f7b33cdd..fdfba858ffc9 100644
> > --- a/arch/x86/um/vdso/vma.c
> > +++ b/arch/x86/um/vdso/vma.c
> > @@ -54,6 +54,7 @@ int arch_setup_additional_pages(struct
> > linux_binprm *bprm, int uses_interp)
> >  {
> >  	struct vm_area_struct *vma;
> >  	struct mm_struct *mm = current->mm;
> > +	unsigned long vm_flags;
> >  	static struct vm_special_mapping vdso_mapping = {
> >  		.name = "[vdso]",
> >  	};
> > @@ -65,9 +66,10 @@ int arch_setup_additional_pages(struct
> > linux_binprm *bprm, int uses_interp)
> >  		return -EINTR;
> > 
> >  	vdso_mapping.pages = vdsop;
> > +	vm_flags =
> > VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC;
> > +	vm_flags |= VM_SEALED_SYSMAP;
> >  	vma = _install_special_mapping(mm, um_vdso_addr,
> > PAGE_SIZE,
> > -		VM_READ|VM_EXEC|
> > -		VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
> > +		vm_flags,
> >  		&vdso_mapping);
> > 
> >  	mmap_write_unlock(mm);
> > --
> > 2.48.1.658.g4767266eb4-goog
> > 

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