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Subject[PATCH V6 35/49] x86/entry: Implement the C version ist_paranoid_entry()
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

It implements the whole ASM version paranoid_entry().

No functional difference intended.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/entry64.c | 37 +++++++++++++++++++++++++++++++++
arch/x86/include/asm/idtentry.h | 3 +++
2 files changed, 40 insertions(+)

diff --git a/arch/x86/entry/entry64.c b/arch/x86/entry/entry64.c
index 60c37dbe650b..dc0bd9dc6d48 100644
--- a/arch/x86/entry/entry64.c
+++ b/arch/x86/entry/entry64.c
@@ -268,3 +268,40 @@ static __always_inline unsigned long ist_switch_to_kernel_gsbase(void)

return ret;
}
+
+/*
+ * Switch and save CR3 in *@cr3 if PTI enabled. Return GSBASE related
+ * information in *@gsbase depending on the availability of the FSGSBASE
+ * instructions:
+ *
+ * FSGSBASE *@gsbase
+ * N 0 -> SWAPGS on exit
+ * 1 -> no SWAPGS on exit
+ *
+ * Y GSBASE value at entry, must be restored in ist_paranoid_exit
+ */
+__visible __entry_text
+void ist_paranoid_entry(unsigned long *cr3, unsigned long *gsbase)
+{
+ /*
+ * Always stash CR3 in *@cr3. This value will be restored,
+ * verbatim, at exit. Needed if ist_paranoid_entry interrupted
+ * another entry that already switched to the user CR3 value
+ * but has not yet returned to userspace.
+ *
+ * This is also why CS (stashed in the "iret frame" by the
+ * hardware at entry) can not be used: this may be a return
+ * to kernel code, but with a user CR3 value.
+ *
+ * Switching CR3 does not depend on kernel GSBASE so it can
+ * be done before switching to the kernel GSBASE. This is
+ * required for FSGSBASE because the kernel GSBASE has to
+ * be retrieved from a kernel internal table.
+ */
+ *cr3 = ist_switch_to_kernel_cr3();
+
+ barrier();
+
+ /* Handle GSBASE, store the return value in *@gsbase for exit. */
+ *gsbase = ist_switch_to_kernel_gsbase();
+}
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 49fabc3e3f0d..f6efa21ec242 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -307,6 +307,9 @@ static __always_inline void __##func(struct pt_regs *regs)
DECLARE_IDTENTRY(vector, func)

#ifdef CONFIG_X86_64
+__visible __entry_text
+void ist_paranoid_entry(unsigned long *cr3, unsigned long *gsbase);
+
/**
* DECLARE_IDTENTRY_IST - Declare functions for IST handling IDT entry points
* @vector: Vector number (ignored for C)
--
2.19.1.6.gb485710b
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