[tip: x86/pasid] x86/traps: Demand-populate PASID MSR via #GP

tip-bot2 for Fenghua Yu
2022-02-15T10:54:39Z

The following commit has been merged into the x86/pasid branch of tip:

Commit-ID: fa6af69f38d3f409bedc55d0112eec36ed526d4b
Gitweb: https://git.kernel.org/tip/fa6af69f38d3f409bedc55d0112eec36ed526d4b
Author: Fenghua Yu <fenghua.yu@intel.com>
AuthorDate: Mon, 07 Feb 2022 15:02:51 -08:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Tue, 15 Feb 2022 11:31:43 +01:00

x86/traps: Demand-populate PASID MSR via #GP

All tasks start with PASID state disabled. This means that the first
time they execute an ENQCMD instruction they will take a #GP fault.

Modify the #GP fault handler to check if the "mm" for the task has
already been allocated a PASID. If so, try to fix the #GP fault by
loading the IA32_PASID MSR.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220207230254.3342514-9-fenghua.yu@intel.com
---
arch/x86/kernel/traps.c | 55 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 55 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c9d566d..7ef00de 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -39,6 +39,7 @@
#include <linux/io.h>
#include <linux/hardirq.h>
#include <linux/atomic.h>
+#include <linux/ioasid.h>

#include <asm/stacktrace.h>
#include <asm/processor.h>
@@ -559,6 +560,57 @@ static bool fixup_iopl_exception(struct pt_regs *regs)
return true;
}

+/*
+ * The unprivileged ENQCMD instruction generates #GPs if the
+ * IA32_PASID MSR has not been populated. If possible, populate
+ * the MSR from a PASID previously allocated to the mm.
+ */
+static bool try_fixup_enqcmd_gp(void)
+{
+#ifdef CONFIG_IOMMU_SVA
+ u32 pasid;
+
+ /*
+ * MSR_IA32_PASID is managed using XSAVE. Directly
+ * writing to the MSR is only possible when fpregs
+ * are valid and the fpstate is not. This is
+ * guaranteed when handling a userspace exception
+ * in *before* interrupts are re-enabled.
+ */
+ lockdep_assert_irqs_disabled();
+
+ /*
+ * Hardware without ENQCMD will not generate
+ * #GPs that can be fixed up here.
+ */
+ if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
+ return false;
+
+ pasid = current->mm->pasid;
+
+ /*
+ * If the mm has not been allocated a
+ * PASID, the #GP can not be fixed up.
+ */
+ if (!pasid_valid(pasid))
+ return false;
+
+ /*
+ * Did this thread already have its PASID activated?
+ * If so, the #GP must be from something else.
+ */
+ if (current->pasid_activated)
+ return false;
+
+ wrmsrl(MSR_IA32_PASID, pasid | MSR_IA32_PASID_VALID);
+ current->pasid_activated = 1;
+
+ return true;
+#else
+ return false;
+#endif
+}
+
DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
{
char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
@@ -567,6 +619,9 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
unsigned long gp_addr;
int ret;

+ if (user_mode(regs) && try_fixup_enqcmd_gp())
+ return;
+
cond_local_irq_enable(regs);

if (static_cpu_has(X86_FEATURE_UMIP)) {