[PATCH 16/30] x86, kaiser: map trace interrupt entry

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

All of the interrupt entry/exit code is in a special section
(.irqentry.text).  This enables the ftrace code to figure out
when the kernel is executing in the "grey area" of interrupt
handling before the C code has taken over and marked the data
structures indicating that an interrupt is in progress.

KAISER needs to map this section into the user page tables
because it contains the assembly that helps us enter interrupt
routines.  In addition to the assembly which KAISER *needs*, the
section also contains the first C function that handles an
interrupt.  This is unfortunate, but it doesn't really hurt
anything.

This patch also aligns the .entry.text and .irqentry.text.  This
ensures that only the _required_ text is mapped.

Without this alignment, code might be mapped inadvertently as a
result of sharing a page with code that is intentionally mapped.
This does not hurt anything, but it makes debugging hard because
random build alignment changes can cause things to fail.

This was missed in the original KAISER patch.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Moritz Lipp <moritz.lipp@xxxxxxxxxxxxxx>
Cc: Daniel Gruss <daniel.gruss@xxxxxxxxxxxxxx>
Cc: Michael Schwarz <michael.schwarz@xxxxxxxxxxxxxx>
Cc: Richard Fellner <richard.fellner@xxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
---

 b/arch/x86/mm/kaiser.c              |   14 ++++++++++++++
 b/include/asm-generic/vmlinux.lds.h |   10 ++++++++++
 2 files changed, 24 insertions(+)

diff -puN arch/x86/mm/kaiser.c~kaiser-user-map-trace-irqentry_text arch/x86/mm/kaiser.c
--- a/arch/x86/mm/kaiser.c~kaiser-user-map-trace-irqentry_text	2017-11-10 11:22:13.763244938 -0800
+++ b/arch/x86/mm/kaiser.c	2017-11-10 11:22:13.768244938 -0800
@@ -30,6 +30,7 @@
 #include <linux/types.h>
 #include <linux/bug.h>
 #include <linux/init.h>
+#include <linux/interrupt.h>
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/uaccess.h>
@@ -382,6 +383,19 @@ void __init kaiser_init(void)
 	 */
 	kaiser_add_user_map_early(get_cpu_gdt_ro(0), PAGE_SIZE,
 				  __PAGE_KERNEL_RO | _PAGE_GLOBAL);
+
+	/*
+	 * .irqentry.text helps us identify code that runs before
+	 * we get a chance to call entering_irq().  This includes
+	 * the interrupt entry assembly plus the first C function
+	 * that gets called.  KAISER does not need the C code
+	 * mapped.  We just use the .irqentry.text section as-is
+	 * to avoid having to carve out a new section for the
+	 * assembly only.
+	 */
+	kaiser_add_user_map_ptrs_early(__irqentry_text_start,
+				       __irqentry_text_end,
+				       __PAGE_KERNEL_RX | _PAGE_GLOBAL);
 }
 
 int kaiser_add_mapping(unsigned long addr, unsigned long size,
diff -puN include/asm-generic/vmlinux.lds.h~kaiser-user-map-trace-irqentry_text include/asm-generic/vmlinux.lds.h
--- a/include/asm-generic/vmlinux.lds.h~kaiser-user-map-trace-irqentry_text	2017-11-10 11:22:13.765244938 -0800
+++ b/include/asm-generic/vmlinux.lds.h	2017-11-10 11:22:13.769244938 -0800
@@ -59,6 +59,12 @@
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)
 
+#ifdef CONFIG_KAISER
+#define ALIGN_KAISER()	. = ALIGN(PAGE_SIZE);
+#else
+#define ALIGN_KAISER()
+#endif
+
 /*
  * LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections, which
  * generates .data.identifier sections, which need to be pulled in with
@@ -493,15 +499,19 @@
 		VMLINUX_SYMBOL(__kprobes_text_end) = .;
 
 #define ENTRY_TEXT							\
+		ALIGN_KAISER();						\
 		ALIGN_FUNCTION();					\
 		VMLINUX_SYMBOL(__entry_text_start) = .;			\
 		*(.entry.text)						\
+		ALIGN_KAISER();						\
 		VMLINUX_SYMBOL(__entry_text_end) = .;
 
 #define IRQENTRY_TEXT							\
+		ALIGN_KAISER();						\
 		ALIGN_FUNCTION();					\
 		VMLINUX_SYMBOL(__irqentry_text_start) = .;		\
 		*(.irqentry.text)					\
+		ALIGN_KAISER();						\
 		VMLINUX_SYMBOL(__irqentry_text_end) = .;
 
 #define SOFTIRQENTRY_TEXT						\
_