[PATCH V8 15/44] x86/pkeys: Preserve the PKS MSR on context switch

ira.weiny
2022-01-27T17:55:24Z

From: Ira Weiny <ira.weiny@intel.com>

The PKS MSR (PKRS) is defined as a per-logical-processor register. This
isolates memory access by logical CPU. Unfortunately, the MSR is not
managed by XSAVE. Therefore, tasks must save/restore the MSR value on
context switch.

Define pks_saved_pkrs in struct thread_struct. Initialize all tasks,
including the init_task, with the PKS_INIT_VALUE when created. Restore
the CPU's MSR to the saved task value on schedule in.

pks_write_current() is added to ensures non-supervisor pkey
configurations compile correctly without pks_saved_pkrs in thread_struct
as well as ensuring CPUs without PKS support are ignored.

NOTE The value of pks_saved_pkrs does not change with this patch. That
is left for future patches.

Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes for V8
From Thomas
Ensure pkrs_write_current() does not suffer the overhead
of preempt disable.
Fix setting of initial value
Remove flawed and broken create_initial_pkrs_value() in
favor of a much simpler and robust macro default
Update function names to be consistent.

s/pkrs_write_current/pks_write_current
This is a more consistent name
s/saved_pkrs/pks_saved_pkrs
s/pkrs_init_value/PKS_INIT_VALUE
Remove pks_init_task()
This function was added mainly to avoid the header file
issue. Adding pks-keys.h solved that and saves the
complexity.

Changes for V7
Move definitions from asm/processor.h to asm/pks.h
s/INIT_PKRS_VALUE/pkrs_init_value
Change pks_init_task()/pks_sched_in() to functions
s/pks_sched_in/pks_write_current to be used more generically
later in the series
---
arch/x86/include/asm/pks.h | 2 ++
arch/x86/include/asm/processor.h | 17 ++++++++++++++++-
arch/x86/kernel/process_64.c | 3 +++
arch/x86/mm/pkeys.c | 13 +++++++++++++
4 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pks.h b/arch/x86/include/asm/pks.h
index 8180fc59790b..d211bf36492c 100644
--- a/arch/x86/include/asm/pks.h
+++ b/arch/x86/include/asm/pks.h
@@ -5,10 +5,12 @@
#ifdef CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS

void pks_setup(void);
+void pks_write_current(void);

#else /* !CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS */

static inline void pks_setup(void) { }
+static inline void pks_write_current(void) { }

#endif /* CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS */

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 2c5f12ae7d04..3530a0e50b4f 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -2,6 +2,8 @@
#ifndef _ASM_X86_PROCESSOR_H
#define _ASM_X86_PROCESSOR_H

+#include <linux/pks-keys.h>
+
#include <asm/processor-flags.h>

/* Forward declaration, a strange C thing */
@@ -502,6 +504,12 @@ struct thread_struct {
unsigned long cr2;
unsigned long trap_nr;
unsigned long error_code;
+
+#ifdef CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS
+ /* Saved Protection key register for supervisor mappings */
+ u32 pks_saved_pkrs;
+#endif
+
#ifdef CONFIG_VM86
/* Virtual 86 mode info */
struct vm86 *vm86;
@@ -769,7 +777,14 @@ static inline void spin_lock_prefetch(const void *x)
#define KSTK_ESP(task) (task_pt_regs(task)->sp)

#else
-#define INIT_THREAD { }
+
+#ifdef CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS
+#define INIT_THREAD { \
+ .pks_saved_pkrs = PKS_INIT_VALUE, \
+}
+#else
+#define INIT_THREAD { }
+#endif

extern unsigned long KSTK_ESP(struct task_struct *task);

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 3402edec236c..81fc0b638308 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -59,6 +59,7 @@
/* Not included via unistd.h */
#include <asm/unistd_32_ia32.h>
#endif
+#include <asm/pks.h>

#include "process.h"

@@ -657,6 +658,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
/* Load the Intel cache allocation PQR MSR. */
resctrl_sched_in();

+ pks_write_current();
+
return prev_p;
}

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index 3dce99ef4127..6d94dfc9a219 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -242,6 +242,19 @@ static inline void pks_write_pkrs(u32 new_pkrs)
}
}

+/**
+ * pks_write_current() - Write the current thread's saved PKRS value
+ *
+ * Context: must be called with preemption disabled
+ */
+void pks_write_current(void)
+{
+ if (!cpu_feature_enabled(X86_FEATURE_PKS))
+ return;
+
+ pks_write_pkrs(current->thread.pks_saved_pkrs);
+}
+
/*
* PKS is independent of PKU and either or both may be supported on a CPU.
*
--
2.31.1