[PATCH 4.9 057/102] arm64: entry: Add exception trampoline page for exceptions from EL0

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@xxxxxxx>

commit c7b9adaf85f8 upstream.

To allow unmapping of the kernel whilst running at EL0, we need to
point the exception vectors at an entry trampoline that can map/unmap
the kernel on entry/exit respectively.

This patch adds the trampoline page, although it is not yet plugged
into the vector table and is therefore unused.

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Tested-by: Laura Abbott <labbott@xxxxxxxxxx>
Tested-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
[Alex: avoid dependency on SW PAN patches]
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx> [v4.9 backport]
[Mark: remove dummy SW PAN definitions]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@xxxxxxx>
Tested-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/entry.S       |   86 ++++++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/vmlinux.lds.S |   17 +++++++
 2 files changed, 103 insertions(+)

--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -29,9 +29,11 @@
 #include <asm/esr.h>
 #include <asm/irq.h>
 #include <asm/memory.h>
+#include <asm/mmu.h>
 #include <asm/thread_info.h>
 #include <asm/asm-uaccess.h>
 #include <asm/unistd.h>
+#include <asm/kernel-pgtable.h>
 
 /*
  * Context tracking subsystem.  Used to instrument transitions
@@ -806,6 +808,90 @@ __ni_sys_trace:
 
 	.popsection				// .entry.text
 
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+/*
+ * Exception vectors trampoline.
+ */
+	.pushsection ".entry.tramp.text", "ax"
+
+	.macro tramp_map_kernel, tmp
+	mrs	\tmp, ttbr1_el1
+	sub	\tmp, \tmp, #SWAPPER_DIR_SIZE
+	bic	\tmp, \tmp, #USER_ASID_FLAG
+	msr	ttbr1_el1, \tmp
+	.endm
+
+	.macro tramp_unmap_kernel, tmp
+	mrs	\tmp, ttbr1_el1
+	add	\tmp, \tmp, #SWAPPER_DIR_SIZE
+	orr	\tmp, \tmp, #USER_ASID_FLAG
+	msr	ttbr1_el1, \tmp
+	/*
+	 * We avoid running the post_ttbr_update_workaround here because the
+	 * user and kernel ASIDs don't have conflicting mappings, so any
+	 * "blessing" as described in:
+	 *
+	 *   http://lkml.kernel.org/r/56BB848A.6060603@xxxxxxxxxxxxxxxxxx
+	 *
+	 * will not hurt correctness. Whilst this may partially defeat the
+	 * point of using split ASIDs in the first place, it avoids
+	 * the hit of invalidating the entire I-cache on every return to
+	 * userspace.
+	 */
+	.endm
+
+	.macro tramp_ventry, regsize = 64
+	.align	7
+1:
+	.if	\regsize == 64
+	msr	tpidrro_el0, x30	// Restored in kernel_ventry
+	.endif
+	tramp_map_kernel	x30
+	ldr	x30, =vectors
+	prfm	plil1strm, [x30, #(1b - tramp_vectors)]
+	msr	vbar_el1, x30
+	add	x30, x30, #(1b - tramp_vectors)
+	isb
+	br	x30
+	.endm
+
+	.macro tramp_exit, regsize = 64
+	adr	x30, tramp_vectors
+	msr	vbar_el1, x30
+	tramp_unmap_kernel	x30
+	.if	\regsize == 64
+	mrs	x30, far_el1
+	.endif
+	eret
+	.endm
+
+	.align	11
+ENTRY(tramp_vectors)
+	.space	0x400
+
+	tramp_ventry
+	tramp_ventry
+	tramp_ventry
+	tramp_ventry
+
+	tramp_ventry	32
+	tramp_ventry	32
+	tramp_ventry	32
+	tramp_ventry	32
+END(tramp_vectors)
+
+ENTRY(tramp_exit_native)
+	tramp_exit
+END(tramp_exit_native)
+
+ENTRY(tramp_exit_compat)
+	tramp_exit	32
+END(tramp_exit_compat)
+
+	.ltorg
+	.popsection				// .entry.tramp.text
+#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
+
 /*
  * Special system call wrappers.
  */
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -56,6 +56,17 @@ jiffies = jiffies_64;
 #define HIBERNATE_TEXT
 #endif
 
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+#define TRAMP_TEXT					\
+	. = ALIGN(PAGE_SIZE);				\
+	VMLINUX_SYMBOL(__entry_tramp_text_start) = .;	\
+	*(.entry.tramp.text)				\
+	. = ALIGN(PAGE_SIZE);				\
+	VMLINUX_SYMBOL(__entry_tramp_text_end) = .;
+#else
+#define TRAMP_TEXT
+#endif
+
 /*
  * The size of the PE/COFF section that covers the kernel image, which
  * runs from stext to _edata, must be a round multiple of the PE/COFF
@@ -128,6 +139,7 @@ SECTIONS
 			HYPERVISOR_TEXT
 			IDMAP_TEXT
 			HIBERNATE_TEXT
+			TRAMP_TEXT
 			*(.fixup)
 			*(.gnu.warning)
 		. = ALIGN(16);
@@ -216,6 +228,11 @@ SECTIONS
 	swapper_pg_dir = .;
 	. += SWAPPER_DIR_SIZE;
 
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+	tramp_pg_dir = .;
+	. += PAGE_SIZE;
+#endif
+
 	_end = .;
 
 	STABS_DEBUG