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>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ca1f93233b22b6c916bb639d88320c9f3230b2ec..905ce1653e82a0591411b6ae370da7937f3b3b79 100644 (file)
--- 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 122d91d4097a24107a1791980030fb4d945a0790..ce985f13dce5d33f4fab1000a071f01c58a798b3 100644 (file)
--- 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 b0768502fa0828aacaedd185a7ab1495471b3720..2da3e478fd8f0020e1a042e4585161d871d3a77e 100644 (file)
--- 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 d5219f2624b7ab363776235c54ba931ece6cada7..41c808d9168a29de5e21ddd7529039a379c2c409 100644 (file)
--- 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 efa0210cf927955902f6ce959c34d397facba546..538ecbc15067001470ff3cd60d2f0ae01339fa9a 100644 (file)
--- 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 c229d9cfe9bf513e0a6aa0a824c4bc9f167c922d..6b70dd625f0198a280ff9d10eaa0141cd1fca2c4 100644 (file)
--- 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 e15b0b64d4d0ef12d13e6a7acf6d4dba7c81b893..1ff18f5fbecb26949a00e14778dbbd0a8ae0d690 100644 (file)
--- 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 0cf86b17714cc9616d96fa288b3aa99c01cd7ff9..e05b3ce1db6b4e7083aad4d36c92a530bd545c17 100644 (file)
--- 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