arm64: Kconfig: Re-jig CONFIG options for 52-bit VA

Enabling 52-bit VAs for userspace is pretty confusing, since it requires
you to select "48-bit" virtual addressing in the Kconfig.

Rework the logic so that 52-bit user virtual addressing is advertised in
the "Virtual address space size" choice, along with some help text to
describe its interaction with Pointer Authentication. The EXPERT-only
option to force all user mappings to the 52-bit range is then made
available immediately below the VA size selection.

Signed-off-by: Will Deacon <will.deacon@arm.com>

8 files changed, 41 insertions, 30 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ca1f93233b22..905ce1653e82 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -682,15 +682,43 @@ config ARM64_VA_BITS_47
 config ARM64_VA_BITS_48
         bool "48-bit"
 
+config ARM64_USER_VA_BITS_52
+        bool "52-bit (user)"
+        depends on ARM64_64K_PAGES && (ARM64_PAN || !ARM64_SW_TTBR0_PAN)
+        help
+          Enable 52-bit virtual addressing for userspace when explicitly
+          requested via a hint to mmap(). The kernel will continue to
+          use 48-bit virtual addresses for its own mappings.
+
+          NOTE: Enabling 52-bit virtual addressing in conjunction with
+          ARMv8.3 Pointer Authentication will result in the PAC being
+          reduced from 7 bits to 3 bits, which may have a significant
+          impact on its susceptibility to brute-force attacks.
+
+          If unsure, select 48-bit virtual addressing instead.
+
 endchoice
 
+config ARM64_FORCE_52BIT
+        bool "Force 52-bit virtual addresses for userspace"
+        depends on ARM64_USER_VA_BITS_52 && EXPERT
+        help
+          For systems with 52-bit userspace VAs enabled, the kernel will attempt
+          to maintain compatibility with older software by providing 48-bit VAs
+          unless a hint is supplied to mmap.
+
+          This configuration option disables the 48-bit compatibility logic, and
+          forces all userspace addresses to be 52-bit on HW that supports it. One
+          should only enable this configuration option for stress testing userspace
+          memory management code. If unsure say N here.
+
 config ARM64_VA_BITS
         int
         default 36 if ARM64_VA_BITS_36
         default 39 if ARM64_VA_BITS_39
         default 42 if ARM64_VA_BITS_42
         default 47 if ARM64_VA_BITS_47
-        default 48 if ARM64_VA_BITS_48
+        default 48 if ARM64_VA_BITS_48 || ARM64_USER_VA_BITS_52
 
 choice
         prompt "Physical address space size"
@@ -716,10 +744,6 @@ config ARM64_PA_BITS_52
 
 endchoice
 
-config ARM64_52BIT_VA
-        def_bool y
-        depends on ARM64_VA_BITS_48 && ARM64_64K_PAGES && (ARM64_PAN || !ARM64_SW_TTBR0_PAN)
-
 config ARM64_PA_BITS
         int
         default 48 if ARM64_PA_BITS_48
@@ -1186,19 +1210,6 @@ config ARM64_CNP
           at runtime, and does not affect PEs that do not implement
           this feature.
 
-config ARM64_FORCE_52BIT
-        bool "Force 52-bit virtual addresses for userspace"
-        depends on ARM64_52BIT_VA && EXPERT
-        help
-          For systems with 52-bit userspace VAs enabled, the kernel will attempt
-          to maintain compatibility with older software by providing 48-bit VAs
-          unless a hint is supplied to mmap.
-
-          This configuration option disables the 48-bit compatibility logic, and
-          forces all userspace addresses to be 52-bit on HW that supports it. One
-          should only enable this configuration option for stress testing userspace
-          memory management code. If unsure say N here.
-
 endmenu
 
 config ARM64_SVE
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 122d91d4097a..ce985f13dce5 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -549,7 +549,7 @@ USER(\label, ic	ivau, \tmp2)			// invalidate I line PoU
  *      ttbr: Value of ttbr to set, modified.
  */
         .macro  offset_ttbr1, ttbr
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
         orr     \ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET
 #endif
         .endm
@@ -560,7 +560,7 @@ USER(\label, ic	ivau, \tmp2)			// invalidate I line PoU
  * to be nop'ed out when dealing with 52-bit kernel VAs.
  */
         .macro  restore_ttbr1, ttbr
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
         bic     \ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET
 #endif
         .endm
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index b0768502fa08..2da3e478fd8f 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -74,7 +74,7 @@ extern u64 idmap_ptrs_per_pgd;
 
 static inline bool __cpu_uses_extended_idmap(void)
 {
-        if (IS_ENABLED(CONFIG_ARM64_52BIT_VA))
+        if (IS_ENABLED(CONFIG_ARM64_USER_VA_BITS_52))
                 return false;
 
         return unlikely(idmap_t0sz != TCR_T0SZ(VA_BITS));
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index d5219f2624b7..41c808d9168a 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -80,7 +80,7 @@
 #define PGDIR_SHIFT             ARM64_HW_PGTABLE_LEVEL_SHIFT(4 - CONFIG_PGTABLE_LEVELS)
 #define PGDIR_SIZE              (_AC(1, UL) << PGDIR_SHIFT)
 #define PGDIR_MASK              (~(PGDIR_SIZE-1))
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
 #define PTRS_PER_PGD            (1 << (52 - PGDIR_SHIFT))
 #else
 #define PTRS_PER_PGD            (1 << (VA_BITS - PGDIR_SHIFT))
@@ -310,7 +310,7 @@
 #define TTBR_BADDR_MASK_52      (((UL(1) << 46) - 1) << 2)
 #endif
 
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
 /* Must be at least 64-byte aligned to prevent corruption of the TTBR */
 #define TTBR1_BADDR_4852_OFFSET (((UL(1) << (52 - PGDIR_SHIFT)) - \
                                  (UL(1) << (48 - PGDIR_SHIFT))) * 8)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index efa0210cf927..538ecbc15067 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -20,11 +20,11 @@
 #define __ASM_PROCESSOR_H
 
 #define KERNEL_DS               UL(-1)
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
 #define USER_DS                 ((UL(1) << 52) - 1)
 #else
 #define USER_DS                 ((UL(1) << VA_BITS) - 1)
-#endif /* CONFIG_ARM64_52BIT_VA */
+#endif /* CONFIG_ARM64_USER_VA_BITS_52 */
 
 /*
  * On arm64 systems, unaligned accesses by the CPU are cheap, and so there is
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index c229d9cfe9bf..6b70dd625f01 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -318,7 +318,7 @@ __create_page_tables:
         adrp    x0, idmap_pg_dir
         adrp    x3, __idmap_text_start          // __pa(__idmap_text_start)
 
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
         mrs_s   x6, SYS_ID_AA64MMFR2_EL1
         and     x6, x6, #(0xf << ID_AA64MMFR2_LVA_SHIFT)
         mov     x5, #52
@@ -800,7 +800,7 @@ ENTRY(__enable_mmu)
 ENDPROC(__enable_mmu)
 
 ENTRY(__cpu_secondary_check52bitva)
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
         ldr_l   x0, vabits_user
         cmp     x0, #52
         b.ne    2f
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index e15b0b64d4d0..1ff18f5fbecb 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -139,7 +139,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
                 if (!cpu_online(cpu)) {
                         pr_crit("CPU%u: failed to come online\n", cpu);
 
-                        if (IS_ENABLED(CONFIG_ARM64_52BIT_VA) && va52mismatch)
+                        if (IS_ENABLED(CONFIG_ARM64_USER_VA_BITS_52) && va52mismatch)
                                 pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
 
                         ret = -EIO;
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 0cf86b17714c..e05b3ce1db6b 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -451,8 +451,8 @@ ENTRY(__cpu_setup)
                         TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
                         TCR_TBI0 | TCR_A1
 
-#ifdef CONFIG_ARM64_52BIT_VA
-        ldr_l           x9, vabits_user
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
+        ldr_l           x9, vabits_user
         sub             x9, xzr, x9
         add             x9, x9, #64
 #else