Re: [PATCH v3 6/7] xen/arm: Taint Xen on incompatible DCZID values

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 6 Sep 2021, Bertrand Marquis wrote:
> > On 3 Sep 2021, at 23:49, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> > 
> > On Wed, 25 Aug 2021, Bertrand Marquis wrote:
> >> Use arm64 cpu feature sanitization to TAIN Xen if different DCZID values
> >                                        ^  TAINT
> > 
> > 
> >> are found (ftr_dczid is using only STRICT method).
> >> In this case actual memory being cleaned by DC ZVA operations would be
> >> different depending on the cores which could make a guest zeroing too
> >> much or too little memory if it is merged between CPUs.
> >> 
> >> We could, on processor supporting it, trap access to DCZID_EL0 register
> >               ^ processors
> 
> Could those typos be fixed during commit ?

Yes they can

 
> >> using HFGRTR_EL2 register but this would not solve the case where a
> >> process is being migrated during a copy or if it cached the value of the
> >> register.
> >> 
> >> Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> >> ---
> >> Change in v3: none
> >> Change in v2: Patch introduced in v2
> >> ---
> >> xen/arch/arm/arm64/cpufeature.c  | 14 +++++++++++---
> >> xen/arch/arm/cpufeature.c        |  2 ++
> >> xen/include/asm-arm/cpufeature.h |  8 ++++++++
> >> 3 files changed, 21 insertions(+), 3 deletions(-)
> >> 
> >> diff --git a/xen/arch/arm/arm64/cpufeature.c 
> >> b/xen/arch/arm/arm64/cpufeature.c
> >> index 61f629ebaa..b1936ef1d6 100644
> >> --- a/xen/arch/arm/arm64/cpufeature.c
> >> +++ b/xen/arch/arm/arm64/cpufeature.c
> >> @@ -329,14 +329,11 @@ static const struct arm64_ftr_bits ftr_mvfr2[] = {
> >>    ARM64_FTR_END,
> >> };
> >> 
> >> -#if 0
> >> -/* TODO: handle this when sanitizing cache related registers */
> >> static const struct arm64_ftr_bits ftr_dczid[] = {
> >>    ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, DCZID_DZP_SHIFT, 1, 
> >> 1),
> >>    ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, DCZID_BS_SHIFT, 
> >> 4, 0),
> >>    ARM64_FTR_END,
> >> };
> >> -#endif
> >> 
> >> static const struct arm64_ftr_bits ftr_id_isar0[] = {
> >>    ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 
> >> ID_ISAR0_DIVIDE_SHIFT, 4, 0),
> >> @@ -592,6 +589,17 @@ void update_system_features(const struct cpuinfo_arm 
> >> *new)
> >> 
> >>    SANITIZE_ID_REG(zfr64, 0, aa64zfr0);
> >> 
> >> +  /*
> >> +   * Comment from Linux:
> > 
> > I don't know if I would keep or remove "Comment from Linux"
> 
> I added that because the comment itself does not really apply to Xen.
> I could have rephrased the comment/
> Anyway I have no objection to remove that statement.
> 
> Do I need to send a v2 for that ?

No you don't need to resend just for that or the typos. However if you
are going to resend, then an update would be nice :-)