Re: [PATCH v3 10/12] KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2

From: Will Deacon <will@kernel.org>
To: "Pierre-Clément Tosi" <ptosi@google.com>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Vincent Donnefort <vdonnefort@google.com>
Subject: Re: [PATCH v3 10/12] KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2
Date: Mon, 3 Jun 2024 14:09:31 +0100	[thread overview]
Message-ID: <20240603130930.GA18991@willie-the-truck> (raw)
In-Reply-To: <vk4jfrmlxyoav365rti4rent5ptmxis5d6vjlynr6xs3s4k7h7@2j2dyv6lhcbr>

On Wed, May 29, 2024 at 01:30:15PM +0100, Pierre-Clément Tosi wrote:
> On Mon, May 13, 2024 at 06:30:05PM +0100, Will Deacon wrote:
> > On Fri, May 10, 2024 at 12:26:39PM +0100, Pierre-Clément Tosi wrote:
> > > [...]
> > > 
> > > Use SYM_TYPED_FUNC_START() for __pkvm_init_switch_pgd, as nVHE can't
> > > call it directly and must use a PA function pointer from C (because it
> > > is part of the idmap page), which would trigger a kCFI failure if the
> > > type ID wasn't present.
> > > 
> > > Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> > > ---
> > >  arch/arm64/include/asm/esr.h       |  6 ++++++
> > >  arch/arm64/kvm/handle_exit.c       | 11 +++++++++++
> > >  arch/arm64/kvm/hyp/nvhe/Makefile   |  6 +++---
> > >  arch/arm64/kvm/hyp/nvhe/hyp-init.S |  6 +++++-
> > >  4 files changed, 25 insertions(+), 4 deletions(-)
> > > 
> > >  [...]
> > > 
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> > > index 5a15737b4233..33fb5732ab83 100644
> > > --- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> > > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> > > @@ -5,6 +5,7 @@
> > >   */
> > >  
> > >  #include <linux/arm-smccc.h>
> > > +#include <linux/cfi_types.h>
> > >  #include <linux/linkage.h>
> > >  
> > >  #include <asm/alternative.h>
> > > @@ -268,8 +269,11 @@ SYM_CODE_END(__kvm_handle_stub_hvc)
> > >  /*
> > >   * void __pkvm_init_switch_pgd(struct kvm_nvhe_init_params *params,
> > >   *                             void (*finalize_fn)(void));
> > > + *
> > > + * SYM_TYPED_FUNC_START() allows C to call this ID-mapped function indirectly
> > > + * using a physical pointer without triggering a kCFI failure.
> > >   */
> > > -SYM_FUNC_START(__pkvm_init_switch_pgd)
> > > +SYM_TYPED_FUNC_START(__pkvm_init_switch_pgd)
> > >  	/* Load the inputs from the VA pointer before turning the MMU off */
> > >  	ldr	x5, [x0, #NVHE_INIT_PGD_PA]
> > >  	ldr	x0, [x0, #NVHE_INIT_STACK_HYP_VA]
> > 
> > Unrelated hunk?
> 
> No, this is needed to prevent a kCFI failure at EL2.
> 
> Please let me know if the comment and commit message aren't clear enough.

I'm not disputing that this hunk is needed, but I think it should be
in place before the patch enabling CFI. For example, by merging it in
with patch 2?

Will

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