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Date: Mon, 9 Nov 2020 12:23:01 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: "tglx@...utronix.de"@aserv0122.oracle.com,
"mingo@...hat.com"@aserv0122.oracle.com,
"bp@...en8.de"@aserv0122.oracle.com,
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Cc: "konrad.wilk@...cle.com"@aserv0122.oracle.com,
"jan.setjeeilers@...cle.com"@aserv0122.oracle.com,
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"alexandre.chartre@...cle.com"@aserv0122.oracle.com
Subject: [RFC][PATCH 06/24] x86/pti: Provide C variants of PTI switch CR3 macros
Page Table Isolation (PTI) use assembly macros to switch the CR3
register between kernel and user page-tables. Add C functions which
implement the same features. For now, these C functions are not
used but they will eventually replace using the assembly macros.
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
arch/x86/entry/common.c | 44 +++++++++++++++
arch/x86/include/asm/entry-common.h | 84 +++++++++++++++++++++++++++++
2 files changed, 128 insertions(+)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 7ee15a12c115..d09b1ded5287 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -343,3 +343,47 @@ __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
}
}
#endif /* CONFIG_XEN_PV */
+
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+
+static __always_inline unsigned long save_and_switch_to_kernel_cr3(void)
+{
+ unsigned long cr3, saved_cr3;
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return 0;
+
+ saved_cr3 = cr3 = __read_cr3();
+ if (cr3 & PTI_USER_PGTABLE_MASK) {
+ adjust_kernel_cr3(&cr3);
+ native_write_cr3(cr3);
+ }
+
+ return saved_cr3;
+}
+
+static __always_inline void restore_cr3(unsigned long cr3)
+{
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ if (static_cpu_has(X86_FEATURE_PCID)) {
+ if (cr3 & PTI_USER_PGTABLE_MASK)
+ adjust_user_cr3(&cr3);
+ else
+ cr3 |= X86_CR3_PCID_NOFLUSH;
+ }
+
+ native_write_cr3(cr3);
+}
+
+#else /* CONFIG_PAGE_TABLE_ISOLATION */
+
+static __always_inline unsigned long save_and_switch_to_kernel_cr3(void)
+{
+ return 0;
+}
+
+static __always_inline void restore_cr3(unsigned long cr3) {}
+
+#endif /* CONFIG_PAGE_TABLE_ISOLATION */
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 6fe54b2813c1..b05b212f5ebc 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -7,6 +7,7 @@
#include <asm/nospec-branch.h>
#include <asm/io_bitmap.h>
#include <asm/fpu/api.h>
+#include <asm/tlbflush.h>
/* Check that the stack and regs on entry from user mode are sane. */
static __always_inline void arch_check_user_regs(struct pt_regs *regs)
@@ -81,4 +82,87 @@ static __always_inline void arch_exit_to_user_mode(void)
}
#define arch_exit_to_user_mode arch_exit_to_user_mode
+#ifndef MODULE
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+
+/*
+ * PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two
+ * halves:
+ */
+#define PTI_USER_PGTABLE_BIT PAGE_SHIFT
+#define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT)
+#define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT
+#define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT)
+#define PTI_USER_PGTABLE_AND_PCID_MASK \
+ (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK)
+
+static __always_inline void adjust_kernel_cr3(unsigned long *cr3)
+{
+ if (static_cpu_has(X86_FEATURE_PCID))
+ *cr3 |= X86_CR3_PCID_NOFLUSH;
+
+ /*
+ * Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3
+ * at kernel pagetables.
+ */
+ *cr3 &= ~PTI_USER_PGTABLE_AND_PCID_MASK;
+}
+
+static __always_inline void adjust_user_cr3(unsigned long *cr3)
+{
+ unsigned short mask;
+ unsigned long asid;
+
+ /*
+ * Test if the ASID needs a flush.
+ */
+ asid = *cr3 & 0x7ff;
+ mask = this_cpu_read(cpu_tlbstate.user_pcid_flush_mask);
+ if (mask & (1 << asid)) {
+ /* Flush needed, clear the bit */
+ this_cpu_and(cpu_tlbstate.user_pcid_flush_mask, ~(1 << asid));
+ } else {
+ *cr3 |= X86_CR3_PCID_NOFLUSH;
+ }
+}
+
+static __always_inline void switch_to_kernel_cr3(void)
+{
+ unsigned long cr3;
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ cr3 = __read_cr3();
+ adjust_kernel_cr3(&cr3);
+ native_write_cr3(cr3);
+}
+
+static __always_inline void switch_to_user_cr3(void)
+{
+ unsigned long cr3;
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ cr3 = __read_cr3();
+ if (static_cpu_has(X86_FEATURE_PCID)) {
+ adjust_user_cr3(&cr3);
+ /* Flip the ASID to the user version */
+ cr3 |= PTI_USER_PCID_MASK;
+ }
+
+ /* Flip the PGD to the user version */
+ cr3 |= PTI_USER_PGTABLE_MASK;
+ native_write_cr3(cr3);
+}
+
+#else /* CONFIG_PAGE_TABLE_ISOLATION */
+
+static inline void switch_to_kernel_cr3(void) {}
+static inline void switch_to_user_cr3(void) {}
+
+#endif /* CONFIG_PAGE_TABLE_ISOLATION */
+#endif /* MODULE */
+
#endif
--
2.18.4
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