From: Denis Mukhin <dmukhin@ford.com>
Rewrite emulation_flags_ok() to simplify future modifications.
No functional change intended.
Signed-off-by: Denis Mukhin <dmukhin@ford.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Teddy Astie <teddy.astie@vates.tech>
---
Changes since v4:
- updated commentaries
- added Teddy's R-b, kept Stefano's R-b
---
xen/arch/x86/domain.c | 91 ++++++++++++++++++++++++++++++++++---------
1 file changed, 73 insertions(+), 18 deletions(-)
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 0363ccb384..4f6670ce37 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -743,32 +743,87 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
return 0;
}
+/*
+ * Verify that the domain's emulation flags resolve to a supported configuration.
+ *
+ * This ensures we only allow a known, safe subset of emulation combinations
+ * (for both functionality and security). Arbitrary mixes are likely to cause
+ * errors (e.g., null pointer dereferences).
+ *
+ * NB: use the internal X86_EMU_XXX symbols, not the public XEN_X86_EMU_XXX
+ * symbols.
+ */
static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
{
+ enum {
+ CAP_PV = BIT(0, U),
+ CAP_HVM = BIT(1, U),
+ CAP_HWDOM = BIT(2, U),
+ CAP_DOMU = BIT(3, U),
+ };
+ static const struct {
+ unsigned int caps;
+ uint32_t min;
+ uint32_t opt;
+ } configs[] = {
+#ifdef CONFIG_PV
+ /* PV */
+ {
+ .caps = CAP_PV | CAP_DOMU,
+ .min = 0,
+ .opt = 0,
+ },
+
+ /* PV dom0 */
+ {
+ .caps = CAP_PV | CAP_HWDOM,
+ .min = X86_EMU_PIT,
+ .opt = 0,
+ },
+#endif /* #ifdef CONFIG_PV */
+
+#ifdef CONFIG_HVM
+ /* PVH dom0 */
+ {
+ .caps = CAP_HVM | CAP_HWDOM,
+ .min = X86_EMU_LAPIC | X86_EMU_IOAPIC | X86_EMU_VPCI,
+ .opt = 0,
+ },
+
+ /* HVM domU */
+ {
+ .caps = CAP_HVM | CAP_DOMU,
+ .min = X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ),
+ /* HVM PIRQ feature is user-selectable. */
+ .opt = X86_EMU_USE_PIRQ,
+ },
+
+ /* PVH domU */
+ {
+ .caps = CAP_HVM | CAP_DOMU,
+ .min = X86_EMU_LAPIC,
+ .opt = 0,
+ },
+#endif /* #ifdef CONFIG_HVM */
+ };
+ unsigned int i, caps = is_hardware_domain(d) ? CAP_HWDOM : CAP_DOMU;
+
+ if ( is_pv_domain(d) )
+ caps |= CAP_PV;
+ else if ( is_hvm_domain(d) )
+ caps |= CAP_HVM;
+
#ifdef CONFIG_HVM
/* This doesn't catch !CONFIG_HVM case but it is better than nothing */
BUILD_BUG_ON(X86_EMU_ALL != XEN_X86_EMU_ALL);
#endif
- if ( is_hvm_domain(d) )
- {
- if ( is_hardware_domain(d) &&
- emflags != (X86_EMU_VPCI | X86_EMU_LAPIC | X86_EMU_IOAPIC) )
- return false;
- if ( !is_hardware_domain(d) &&
- /* HVM PIRQ feature is user-selectable. */
- (emflags & ~X86_EMU_USE_PIRQ) !=
- (X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ)) &&
- emflags != X86_EMU_LAPIC )
- return false;
- }
- else if ( emflags != 0 && emflags != X86_EMU_PIT )
- {
- /* PV or classic PVH. */
- return false;
- }
+ for ( i = 0; i < ARRAY_SIZE(configs); i++ )
+ if ( caps == configs[i].caps &&
+ (emflags & ~configs[i].opt) == configs[i].min )
+ return true;
- return true;
+ return false;
}
void __init arch_init_idle_domain(struct domain *d)
--
2.34.1On 02.06.2025 21:17, dmkhn@proton.me wrote:
> From: Denis Mukhin <dmukhin@ford.com>
>
> Rewrite emulation_flags_ok() to simplify future modifications.
>
> No functional change intended.
>
> Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
> Reviewed-by: Teddy Astie <teddy.astie@vates.tech>
> ---
> Changes since v4:
> - updated commentaries
> - added Teddy's R-b, kept Stefano's R-b
> ---
> xen/arch/x86/domain.c | 91 ++++++++++++++++++++++++++++++++++---------
> 1 file changed, 73 insertions(+), 18 deletions(-)
Given this diffstat, I wonder what the other x86 maintainers think about
this.
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -743,32 +743,87 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
> return 0;
> }
>
> +/*
> + * Verify that the domain's emulation flags resolve to a supported configuration.
> + *
> + * This ensures we only allow a known, safe subset of emulation combinations
> + * (for both functionality and security). Arbitrary mixes are likely to cause
> + * errors (e.g., null pointer dereferences).
> + *
> + * NB: use the internal X86_EMU_XXX symbols, not the public XEN_X86_EMU_XXX
> + * symbols.
> + */
> static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
> {
> + enum {
> + CAP_PV = BIT(0, U),
> + CAP_HVM = BIT(1, U),
> + CAP_HWDOM = BIT(2, U),
> + CAP_DOMU = BIT(3, U),
> + };
> + static const struct {
> + unsigned int caps;
> + uint32_t min;
> + uint32_t opt;
> + } configs[] = {
> +#ifdef CONFIG_PV
> + /* PV */
> + {
> + .caps = CAP_PV | CAP_DOMU,
> + .min = 0,
> + .opt = 0,
Why the latter two initializers? Imo adding ones which say nothing else than
what's the default is only enlarging code without much real benefit.
> + },
> +
> + /* PV dom0 */
> + {
> + .caps = CAP_PV | CAP_HWDOM,
> + .min = X86_EMU_PIT,
> + .opt = 0,
> + },
> +#endif /* #ifdef CONFIG_PV */
> +
> +#ifdef CONFIG_HVM
> + /* PVH dom0 */
> + {
> + .caps = CAP_HVM | CAP_HWDOM,
> + .min = X86_EMU_LAPIC | X86_EMU_IOAPIC | X86_EMU_VPCI,
> + .opt = 0,
> + },
> +
> + /* HVM domU */
> + {
> + .caps = CAP_HVM | CAP_DOMU,
> + .min = X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ),
> + /* HVM PIRQ feature is user-selectable. */
> + .opt = X86_EMU_USE_PIRQ,
> + },
> +
> + /* PVH domU */
> + {
> + .caps = CAP_HVM | CAP_DOMU,
> + .min = X86_EMU_LAPIC,
> + .opt = 0,
> + },
> +#endif /* #ifdef CONFIG_HVM */
> + };
> + unsigned int i, caps = is_hardware_domain(d) ? CAP_HWDOM : CAP_DOMU;
> +
> + if ( is_pv_domain(d) )
> + caps |= CAP_PV;
> + else if ( is_hvm_domain(d) )
> + caps |= CAP_HVM;
There's no 3rd case, so this could be expressed with plain "else", and hence
also with a conditional operator, and hence could also be right in the
initializer. How far to go with those transformations I'm not sure; personally
I'd go all the way, but I'd be okay-ish with just the first of the steps.
Jan
On Wed, Jun 04, 2025 at 12:43:22PM +0200, Jan Beulich wrote:
> On 02.06.2025 21:17, dmkhn@proton.me wrote:
> > From: Denis Mukhin <dmukhin@ford.com>
> >
> > Rewrite emulation_flags_ok() to simplify future modifications.
> >
> > No functional change intended.
> >
> > Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> > Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
> > Reviewed-by: Teddy Astie <teddy.astie@vates.tech>
> > ---
> > Changes since v4:
> > - updated commentaries
> > - added Teddy's R-b, kept Stefano's R-b
> > ---
> > xen/arch/x86/domain.c | 91 ++++++++++++++++++++++++++++++++++---------
> > 1 file changed, 73 insertions(+), 18 deletions(-)
>
> Given this diffstat, I wonder what the other x86 maintainers think about
> this.
I think the array is a cleaner way of expressing the possible domain
configurations.
See below, I got some suggestions that would likely make the diffstat
better.
> > --- a/xen/arch/x86/domain.c
> > +++ b/xen/arch/x86/domain.c
> > @@ -743,32 +743,87 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
> > return 0;
> > }
> >
> > +/*
> > + * Verify that the domain's emulation flags resolve to a supported configuration.
> > + *
> > + * This ensures we only allow a known, safe subset of emulation combinations
> > + * (for both functionality and security). Arbitrary mixes are likely to cause
> > + * errors (e.g., null pointer dereferences).
> > + *
> > + * NB: use the internal X86_EMU_XXX symbols, not the public XEN_X86_EMU_XXX
> > + * symbols.
> > + */
> > static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
> > {
> > + enum {
> > + CAP_PV = BIT(0, U),
> > + CAP_HVM = BIT(1, U),
> > + CAP_HWDOM = BIT(2, U),
> > + CAP_DOMU = BIT(3, U),
> > + };
> > + static const struct {
> > + unsigned int caps;
> > + uint32_t min;
> > + uint32_t opt;
> > + } configs[] = {
> > +#ifdef CONFIG_PV
> > + /* PV */
> > + {
> > + .caps = CAP_PV | CAP_DOMU,
> > + .min = 0,
> > + .opt = 0,
>
> Why the latter two initializers? Imo adding ones which say nothing else than
> what's the default is only enlarging code without much real benefit.
I'm fine with skipping explicit initialization of 0 fields, I don't
think there's much benefit here.
> > + },
> > +
> > + /* PV dom0 */
> > + {
> > + .caps = CAP_PV | CAP_HWDOM,
> > + .min = X86_EMU_PIT,
> > + .opt = 0,
> > + },
> > +#endif /* #ifdef CONFIG_PV */
I think the above two elements could be folded into a single one,
iow:
/* PV domU and dom0 */
{
.caps = CAP_PV
.min = X86_EMU_PIT,
},
As given the current code we do allow PV domUs with X86_EMU_PIT, so
otherwise the change here is not non-functional.
> > +
> > +#ifdef CONFIG_HVM
> > + /* PVH dom0 */
> > + {
> > + .caps = CAP_HVM | CAP_HWDOM,
> > + .min = X86_EMU_LAPIC | X86_EMU_IOAPIC | X86_EMU_VPCI,
> > + .opt = 0,
> > + },
> > +
> > + /* HVM domU */
> > + {
> > + .caps = CAP_HVM | CAP_DOMU,
> > + .min = X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ),
> > + /* HVM PIRQ feature is user-selectable. */
> > + .opt = X86_EMU_USE_PIRQ,
> > + },
> > +
> > + /* PVH domU */
> > + {
> > + .caps = CAP_HVM | CAP_DOMU,
> > + .min = X86_EMU_LAPIC,
> > + .opt = 0,
> > + },
> > +#endif /* #ifdef CONFIG_HVM */
> > + };
> > + unsigned int i, caps = is_hardware_domain(d) ? CAP_HWDOM : CAP_DOMU;
> > +
> > + if ( is_pv_domain(d) )
> > + caps |= CAP_PV;
> > + else if ( is_hvm_domain(d) )
> > + caps |= CAP_HVM;
>
> There's no 3rd case, so this could be expressed with plain "else", and hence
> also with a conditional operator, and hence could also be right in the
> initializer. How far to go with those transformations I'm not sure; personally
> I'd go all the way, but I'd be okay-ish with just the first of the steps.
I agree, I would place them all in the definition:
unsigned int caps = (is_hardware_domain(d) ? CAP_HWDOM : CAP_DOMU) |
(is_pv_domain(d) ? CAP_PV : CAP_HVM);
Thanks, Roger.
On Wed, Jun 04, 2025 at 12:43:22PM +0200, Jan Beulich wrote:
> On 02.06.2025 21:17, dmkhn@proton.me wrote:
> > From: Denis Mukhin <dmukhin@ford.com>
> >
> > Rewrite emulation_flags_ok() to simplify future modifications.
> >
> > No functional change intended.
> >
> > Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> > Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
> > Reviewed-by: Teddy Astie <teddy.astie@vates.tech>
> > ---
> > Changes since v4:
> > - updated commentaries
> > - added Teddy's R-b, kept Stefano's R-b
> > ---
> > xen/arch/x86/domain.c | 91 ++++++++++++++++++++++++++++++++++---------
> > 1 file changed, 73 insertions(+), 18 deletions(-)
>
> Given this diffstat, I wonder what the other x86 maintainers think about
> this.
>
> > --- a/xen/arch/x86/domain.c
> > +++ b/xen/arch/x86/domain.c
> > @@ -743,32 +743,87 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
> > return 0;
> > }
> >
> > +/*
> > + * Verify that the domain's emulation flags resolve to a supported configuration.
> > + *
> > + * This ensures we only allow a known, safe subset of emulation combinations
> > + * (for both functionality and security). Arbitrary mixes are likely to cause
> > + * errors (e.g., null pointer dereferences).
> > + *
> > + * NB: use the internal X86_EMU_XXX symbols, not the public XEN_X86_EMU_XXX
> > + * symbols.
> > + */
> > static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
> > {
> > + enum {
> > + CAP_PV = BIT(0, U),
> > + CAP_HVM = BIT(1, U),
> > + CAP_HWDOM = BIT(2, U),
> > + CAP_DOMU = BIT(3, U),
> > + };
> > + static const struct {
> > + unsigned int caps;
> > + uint32_t min;
> > + uint32_t opt;
> > + } configs[] = {
> > +#ifdef CONFIG_PV
> > + /* PV */
> > + {
> > + .caps = CAP_PV | CAP_DOMU,
> > + .min = 0,
> > + .opt = 0,
>
> Why the latter two initializers? Imo adding ones which say nothing else than
> what's the default is only enlarging code without much real benefit.
Sure, no problem, I can address that.
Thanks!
>
> > + },
> > +
> > + /* PV dom0 */
> > + {
> > + .caps = CAP_PV | CAP_HWDOM,
> > + .min = X86_EMU_PIT,
> > + .opt = 0,
> > + },
> > +#endif /* #ifdef CONFIG_PV */
> > +
> > +#ifdef CONFIG_HVM
> > + /* PVH dom0 */
> > + {
> > + .caps = CAP_HVM | CAP_HWDOM,
> > + .min = X86_EMU_LAPIC | X86_EMU_IOAPIC | X86_EMU_VPCI,
> > + .opt = 0,
> > + },
> > +
> > + /* HVM domU */
> > + {
> > + .caps = CAP_HVM | CAP_DOMU,
> > + .min = X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ),
> > + /* HVM PIRQ feature is user-selectable. */
> > + .opt = X86_EMU_USE_PIRQ,
> > + },
> > +
> > + /* PVH domU */
> > + {
> > + .caps = CAP_HVM | CAP_DOMU,
> > + .min = X86_EMU_LAPIC,
> > + .opt = 0,
> > + },
> > +#endif /* #ifdef CONFIG_HVM */
> > + };
> > + unsigned int i, caps = is_hardware_domain(d) ? CAP_HWDOM : CAP_DOMU;
> > +
> > + if ( is_pv_domain(d) )
> > + caps |= CAP_PV;
> > + else if ( is_hvm_domain(d) )
> > + caps |= CAP_HVM;
>
> There's no 3rd case, so this could be expressed with plain "else", and hence
> also with a conditional operator, and hence could also be right in the
> initializer. How far to go with those transformations I'm not sure; personally
> I'd go all the way, but I'd be okay-ish with just the first of the steps.
Ack.
>
> Jan
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