FROMLIST: BACKPORT: arm64: Introduce uaccess_{disable,enable} functionality based on TTBR0_EL1
This patch adds the uaccess macros/functions to disable access to user
space by setting TTBR0_EL1 to a reserved zeroed page. Since the value
written to TTBR0_EL1 must be a physical address, for simplicity this
patch introduces a reserved_ttbr0 page at a constant offset from
swapper_pg_dir. The uaccess_disable code uses the ttbr1_el1 value
adjusted by the reserved_ttbr0 offset.
Enabling access to user is done by restoring TTBR0_EL1 with the value
from the struct thread_info ttbr0 variable. Interrupts must be disabled
during the uaccess_ttbr0_enable code to ensure the atomicity of the
thread_info.ttbr0 read and TTBR0_EL1 write. This patch also moves the
get_thread_info asm macro from entry.S to assembler.h for reuse in the
uaccess_ttbr0_* macros.
Cc: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Change-Id: Idf09a870b8612dce23215bce90d88781f0c0c3aa
(cherry picked from commit 940d37234182d2675ab8ab46084840212d735018)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
[Backport]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index ab87006..359d9d2 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -41,6 +41,15 @@
msr daifclr, #2
.endm
+ .macro save_and_disable_irq, flags
+ mrs \flags, daif
+ msr daifset, #2
+ .endm
+
+ .macro restore_irq, flags
+ msr daif, \flags
+ .endm
+
/*
* Enable and disable debug exceptions.
*/
@@ -396,6 +405,13 @@
.endm
/*
+ * Return the current thread_info.
+ */
+ .macro get_thread_info, rd
+ mrs \rd, sp_el0
+ .endm
+
+/*
* Errata workaround post TTBR0_EL1 update.
*/
.macro post_ttbr0_update_workaround
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index a27c324..e5cfb73 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -226,6 +226,12 @@
return id_aa64mmfr0_mixed_endian_el0(read_system_reg(SYS_ID_AA64MMFR0_EL1));
}
+static inline bool system_uses_ttbr0_pan(void)
+{
+ return IS_ENABLED(CONFIG_ARM64_SW_TTBR0_PAN) &&
+ !cpus_have_cap(ARM64_HAS_PAN);
+}
+
#endif /* __ASSEMBLY__ */
#endif
diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index 7e51d1b..7803343 100644
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -19,6 +19,7 @@
#ifndef __ASM_KERNEL_PGTABLE_H
#define __ASM_KERNEL_PGTABLE_H
+#include <asm/pgtable.h>
#include <asm/sparsemem.h>
/*
@@ -54,6 +55,12 @@
#define SWAPPER_DIR_SIZE (SWAPPER_PGTABLE_LEVELS * PAGE_SIZE)
#define IDMAP_DIR_SIZE (IDMAP_PGTABLE_LEVELS * PAGE_SIZE)
+#ifdef CONFIG_ARM64_SW_TTBR0_PAN
+#define RESERVED_TTBR0_SIZE (PAGE_SIZE)
+#else
+#define RESERVED_TTBR0_SIZE (0)
+#endif
+
/* Initial memory map size */
#if ARM64_SWAPPER_USES_SECTION_MAPS
#define SWAPPER_BLOCK_SHIFT SECTION_SHIFT
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index e9ea5a6..33e454e 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -47,6 +47,9 @@
struct thread_info {
unsigned long flags; /* low level flags */
mm_segment_t addr_limit; /* address limit */
+#ifdef CONFIG_ARM64_SW_TTBR0_PAN
+ u64 ttbr0; /* saved TTBR0_EL1 */
+#endif
struct task_struct *task; /* main task structure */
int preempt_count; /* 0 => preemptable, <0 => bug */
int cpu; /* cpu */
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 1636973..9e06272 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -30,6 +30,7 @@
#include <asm/alternative.h>
#include <asm/cpufeature.h>
+#include <asm/kernel-pgtable.h>
#include <asm/ptrace.h>
#include <asm/sysreg.h>
#include <asm/errno.h>
@@ -124,16 +125,57 @@
/*
* User access enabling/disabling.
*/
+#ifdef CONFIG_ARM64_SW_TTBR0_PAN
+static inline void uaccess_ttbr0_disable(void)
+{
+ unsigned long ttbr;
+
+ /* reserved_ttbr0 placed at the end of swapper_pg_dir */
+ ttbr = read_sysreg(ttbr1_el1) + SWAPPER_DIR_SIZE;
+ write_sysreg(ttbr, ttbr0_el1);
+ isb();
+}
+
+static inline void uaccess_ttbr0_enable(void)
+{
+ unsigned long flags;
+
+ /*
+ * Disable interrupts to avoid preemption between reading the 'ttbr0'
+ * variable and the MSR. A context switch could trigger an ASID
+ * roll-over and an update of 'ttbr0'.
+ */
+ local_irq_save(flags);
+ write_sysreg(current_thread_info()->ttbr0, ttbr0_el1);
+ isb();
+ local_irq_restore(flags);
+}
+#else
+static inline void uaccess_ttbr0_disable(void)
+{
+}
+
+static inline void uaccess_ttbr0_enable(void)
+{
+}
+#endif
+
#define __uaccess_disable(alt) \
do { \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), alt, \
- CONFIG_ARM64_PAN)); \
+ if (system_uses_ttbr0_pan()) \
+ uaccess_ttbr0_disable(); \
+ else \
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), alt, \
+ CONFIG_ARM64_PAN)); \
} while (0)
#define __uaccess_enable(alt) \
do { \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), alt, \
- CONFIG_ARM64_PAN)); \
+ if (system_uses_ttbr0_pan()) \
+ uaccess_ttbr0_enable(); \
+ else \
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), alt, \
+ CONFIG_ARM64_PAN)); \
} while (0)
static inline void uaccess_disable(void)
@@ -371,12 +413,39 @@
#include <asm/alternative.h>
#include <asm/assembler.h>
+#include <asm/kernel-pgtable.h>
/*
- * User access enabling/disabling macros. These are no-ops when UAO is
- * present.
+ * User access enabling/disabling macros.
+ */
+ .macro uaccess_ttbr0_disable, tmp1
+ mrs \tmp1, ttbr1_el1 // swapper_pg_dir
+ add \tmp1, \tmp1, #SWAPPER_DIR_SIZE // reserved_ttbr0 at the end of swapper_pg_dir
+ msr ttbr0_el1, \tmp1 // set reserved TTBR0_EL1
+ isb
+ .endm
+
+ .macro uaccess_ttbr0_enable, tmp1
+ get_thread_info \tmp1
+ ldr \tmp1, [\tmp1, #TI_TTBR0] // load saved TTBR0_EL1
+ msr ttbr0_el1, \tmp1 // set the non-PAN TTBR0_EL1
+ isb
+ .endm
+
+/*
+ * These macros are no-ops when UAO is present.
*/
.macro uaccess_disable_not_uao, tmp1
+#ifdef CONFIG_ARM64_SW_TTBR0_PAN
+alternative_if_not ARM64_HAS_PAN
+ uaccess_ttbr0_disable \tmp1
+alternative_else
+ nop
+ nop
+ nop
+ nop
+alternative_endif
+#endif
alternative_if_not ARM64_ALT_PAN_NOT_UAO
nop
alternative_else
@@ -385,6 +454,21 @@
.endm
.macro uaccess_enable_not_uao, tmp1, tmp2
+#ifdef CONFIG_ARM64_SW_TTBR0_PAN
+alternative_if_not ARM64_HAS_PAN
+ save_and_disable_irq \tmp2 // avoid preemption
+ uaccess_ttbr0_enable \tmp1
+ restore_irq \tmp2
+alternative_else
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+alternative_endif
+#endif
alternative_if_not ARM64_ALT_PAN_NOT_UAO
nop
alternative_else