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From: Rik van Riel <riel@surriel.com>
Date: Sun, 9 Sep 2018 18:30:47 +0200
Subject: [PATCH 15/27] x86/fpu: Eager switch PKRU state
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.10-rt7.tar.xz
While most of a task's FPU state is only needed in user space, the
protection keys need to be in place immediately after a context switch.
The reason is that any access to userspace memory while running in
kernel mode also need to abide by the memory permissions specified in
the protection keys.
The "eager switch" is a preparation for loading the FPU state on return
to userland. Instead of decoupling PKRU state from xstate I update PKRU
within xstate on write operations by the kernel.
The read/write_pkru() is moved to another header file so it can easily
accessed from pgtable.h and fpu/internal.h.
For user tasks we should always get the PKRU from the xsave area and it
should not change anything because the PKRU value was loaded as part of
FPU restore.
For kernel threads we now will have the default "init_pkru_value"
written. Before this commit the kernel thread would end up with a
random value which it inherited from the previous user task.
Signed-off-by: Rik van Riel <riel@surriel.com>
[bigeasy: save pkru to xstate, no cache, don't use __raw_xsave_addr()]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/x86/include/asm/fpu/internal.h | 24 ++++++++++++++++++++++--
arch/x86/include/asm/fpu/xstate.h | 1 +
arch/x86/include/asm/pgtable.h | 6 ++++++
arch/x86/mm/pkeys.c | 1 -
4 files changed, 29 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -14,6 +14,7 @@
#include <linux/compat.h>
#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/mm.h>
#include <asm/user.h>
#include <asm/fpu/api.h>
@@ -562,8 +563,27 @@ switch_fpu_prepare(struct fpu *old_fpu,
*/
static inline void switch_fpu_finish(struct fpu *new_fpu, int cpu)
{
- if (static_cpu_has(X86_FEATURE_FPU))
- __fpregs_load_activate(new_fpu, cpu);
+ struct pkru_state *pk;
+ u32 pkru_val = init_pkru_value;
+
+ if (!static_cpu_has(X86_FEATURE_FPU))
+ return;
+
+ __fpregs_load_activate(new_fpu, cpu);
+
+ if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
+ return;
+
+ /*
+ * PKRU state is switched eagerly because it needs to be valid before we
+ * return to userland e.g. for a copy_to_user() operation.
+ */
+ if (current->mm) {
+ pk = get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU);
+ if (pk)
+ pkru_val = pk->pkru;
+ }
+ __write_pkru(pkru_val);
}
/*
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -5,6 +5,7 @@
#include <linux/types.h>
#include <asm/processor.h>
#include <linux/uaccess.h>
+#include <asm/user.h>
/* Bit 63 of XCR0 is reserved for future expansion */
#define XFEATURE_MASK_EXTEND (~(XFEATURE_MASK_FPSSE | (1ULL << 63)))
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1355,6 +1355,12 @@ static inline pmd_t pmd_swp_clear_soft_d
#define PKRU_WD_BIT 0x2
#define PKRU_BITS_PER_PKEY 2
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+extern u32 init_pkru_value;
+#else
+#define init_pkru_value 0
+#endif
+
static inline bool __pkru_allows_read(u32 pkru, u16 pkey)
{
int pkru_pkey_bits = pkey * PKRU_BITS_PER_PKEY;
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -126,7 +126,6 @@ int __arch_override_mprotect_pkey(struct
* in the process's lifetime will not accidentally get access
* to data which is pkey-protected later on.
*/
-static
u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) |
PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) |
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