RE: [PATCH 02/10] x86/efi: Return error status if mapping EFI regions fail

Prakhya, Sai Praneeth
2019-02-04T22:29:40Z

> > > efi_map_region() creates VA mappings for an given EFI region using
> > > any one of the two helper functions (namely __map_region() and
> old_map_region()).
> > > These helper functions *could* fail while creating mappings and
> > > presently their return value is not checked. Not checking for the
> > > return value of these functions might create issues because after
> > > these functions return "md->virt_addr" is set to the requested
> > > virtual address (so it's assumed that these functions always succeed
> > > which is not quite true). This assumption leads to "md->virt_addr"
> > > having invalid mapping should any of
> > > __map_region() or old_map_region() fail.
> > >
> > > Hence, check for the return value of these functions and if indeed
> > > they fail, turn off EFI Runtime Services forever because kernel
> > > cannot prioritize among EFI regions.
> > >
[...................]
> > > -void __init old_map_region(efi_memory_desc_t *md)
> > > +int __init old_map_region(efi_memory_desc_t *md)
> > > {
> > > u64 start_pfn, end_pfn, end;
> > > unsigned long size;
> > > @@ -601,10 +601,14 @@ void __init old_map_region(efi_memory_desc_t
> *md)
> > > va = efi_ioremap(md->phys_addr, size,
> > > md->type, md->attribute);
> > >
> > > - md->virt_addr = (u64) (unsigned long) va;
> > > - if (!va)
> > > + if (!va) {
> > > pr_err("ioremap of 0x%llX failed!\n",
> > > (unsigned long long)md->phys_addr);
> > > + return -ENOMEM;
> > > + }
> > > +
> > > + md->virt_addr = (u64)(unsigned long)va;
> > > + return 0;
> >
> > Just wondering, shouldn't the failure path set ->virt_addr to
> > something safe, just in case a caller doesn't check the error and relies on it?
> >
> > That's because in this commit we've now changed it from 0 to undefined.
> >
>
> Indeed. We don't usually rely on the value of ->virt_addr when
> EFI_RUNTIME_SERVICES is unset, but there is some sysfs code, and perhaps
> some other places where we do reference ->virt_addr, and not assigning it at all
> is obviously wrong, and potentially hazardous.
>

Ok.. makes sense.
Do you think md->virt_addr = 0 for fail case is ok?

> > > +int __init efi_map_region_fixed(efi_memory_desc_t *md) { return 0;
> > > +}
> >
> > Inline functions should be marked inline ...
> >
> > > if (efi_va < EFI_VA_END) {
> > > - pr_warn(FW_WARN "VA address range overflow!\n");
> > > - return;
> > > + pr_err(FW_WARN "VA address range overflow!\n");
> > > + return -ENOMEM;
> > > }
> > >
> > > /* Do the VA map */
> > > - __map_region(md, efi_va);
> > > + if (__map_region(md, efi_va))
> > > + return -ENOMEM;
> > > +
> > > md->virt_addr = efi_va;
> > > + return 0;
> >
> > Same error return problem of leaving ->virt_addr undefined.
> >

Sure! Will fix it in V2.

> > Note that I also fixed up the grammar and readability of the changelog
> > - see the updated version below.

Thanks for fixing :)

> >
> > Thanks,
> >
> > Ingo
> >
> > =============>
> > Subject: x86/efi: Return error status if mapping of EFI regions fails
> > From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Date: Sat, 2 Feb 2019 10:41:11 +0100
> >
> > From: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> >
> > efi_map_region() creates VA mappings for a given EFI region using one
> > of the two helper functions (namely __map_region() and old_map_region()).
> >
> > These helper functions could fail while creating mappings and
> > presently their return value is not checked.
> >
> > Not checking for the return value of these functions might create
> > bugs, because after these functions return "md->virt_addr" is set to
> > the requested virtual address (so it's assumed that these functions
> > always succeed which is not quite true). This assumption leads to
> > "md->virt_addr" having invalid mapping, should any of __map_region()
> > or old_map_region() fail.
> >
> > Hence, check for the return value of these functions and if indeed
> > they fail, turn off EFI Runtime Services forever because kernel cannot
> > prioritize among EFI regions.
> >
> > This also fixes the comment "FIXME: add error handling" in
> > kexec_enter_virtual_mode().
> >
>
> Thanks Ingo.
>
> Sai, could you please respin this and use Ingo's updated version of the commit
> log?

Sure! I will send a V2 with the mentioned changes.

Regards,
Sai