From 8d2de4223557f020236873a01ce95a9e9771f467 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Fri, 1 Jul 2016 16:53:00 +0100 Subject: [PATCH] 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 Cc: James Morse Cc: Kees Cook Cc: Mark Rutland Signed-off-by: Catalin Marinas Bug: 31432001 Change-Id: I54ada623160cb47f5762e0e39a5e84a75252dbfd (cherry picked from commit 4b65a5db362783ab4b04ca1c1d2ad70ed9b0ba2a) Signed-off-by: Sami Tolvanen --- arch/arm64/include/asm/assembler.h | 16 ++++ arch/arm64/include/asm/cpufeature.h | 6 ++ arch/arm64/include/asm/kernel-pgtable.h | 7 ++ arch/arm64/include/asm/thread_info.h | 3 + arch/arm64/include/asm/uaccess.h | 108 ++++++++++++++++++++++-- arch/arm64/kernel/asm-offsets.c | 3 + arch/arm64/kernel/cpufeature.c | 1 + arch/arm64/kernel/entry.S | 4 - arch/arm64/kernel/head.S | 6 +- arch/arm64/kernel/vmlinux.lds.S | 5 ++ 10 files changed, 146 insertions(+), 13 deletions(-) diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index 7b2a8925ac86..d8855ca6068a 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -53,6 +53,15 @@ 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. */ @@ -371,6 +380,13 @@ alternative_endif movk \reg, :abs_g0_nc:\val .endm +/* + * Return the current thread_info. + */ + .macro get_thread_info, rd + mrs \rd, sp_el0 + .endm + /* * Errata workaround post TTBR0_EL1 update. */ diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 1695f77d8bf2..8e1f826caf99 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -189,6 +189,12 @@ static inline bool system_supports_mixed_endian_el0(void) 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 7e51d1b57c0c..7803343e5881 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 #include /* @@ -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 abd64bd1f6d9..794d22603f04 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -48,6 +48,9 @@ struct thread_info { unsigned long flags; /* low level flags */ mm_segment_t addr_limit; /* address limit */ struct task_struct *task; /* main task structure */ +#ifdef CONFIG_ARM64_SW_TTBR0_PAN + u64 ttbr0; /* saved TTBR0_EL1 */ +#endif 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 8259eded53dc..955c6e58a624 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -19,6 +19,7 @@ #define __ASM_UACCESS_H #include +#include #include #ifndef __ASSEMBLY__ @@ -129,16 +130,71 @@ static inline void set_fs(mm_segment_t fs) /* * 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); +} + +static inline bool uaccess_ttbr0_disable(void) +{ + if (!system_uses_ttbr0_pan()) + return false; + __uaccess_ttbr0_disable(); + return true; +} + +static inline bool uaccess_ttbr0_enable(void) +{ + if (!system_uses_ttbr0_pan()) + return false; + __uaccess_ttbr0_enable(); + return true; +} +#else +static inline bool uaccess_ttbr0_disable(void) +{ + return false; +} + +static inline bool uaccess_ttbr0_enable(void) +{ + return false; +} +#endif + #define __uaccess_disable(alt) \ do { \ - asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), alt, \ - CONFIG_ARM64_PAN)); \ + if (!uaccess_ttbr0_disable()) \ + 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 (uaccess_ttbr0_enable()) \ + asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), alt, \ + CONFIG_ARM64_PAN)); \ } while (0) static inline void uaccess_disable(void) @@ -369,16 +425,56 @@ extern __must_check long strnlen_user(const char __user *str, long n); #include /* - * User access enabling/disabling macros. These are no-ops when UAO is - * present. + * User access enabling/disabling macros. + */ +#ifdef CONFIG_ARM64_SW_TTBR0_PAN + .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, #TSK_TI_TTBR0] // load saved TTBR0_EL1 + msr ttbr0_el1, \tmp1 // set the non-PAN TTBR0_EL1 + isb + .endm + + .macro uaccess_ttbr0_disable, tmp1 +alternative_if_not ARM64_HAS_PAN + __uaccess_ttbr0_disable \tmp1 +alternative_else_nop_endif + .endm + + .macro uaccess_ttbr0_enable, tmp1, tmp2 +alternative_if_not ARM64_HAS_PAN + save_and_disable_irq \tmp2 // avoid preemption + __uaccess_ttbr0_enable \tmp1 + restore_irq \tmp2 +alternative_else_nop_endif + .endm +#else + .macro uaccess_ttbr0_disable, tmp1 + .endm + + .macro uaccess_ttbr0_enable, tmp1, tmp2 + .endm +#endif + +/* + * These macros are no-ops when UAO is present. */ .macro uaccess_disable_not_uao, tmp1 + uaccess_ttbr0_disable \tmp1 alternative_if ARM64_ALT_PAN_NOT_UAO SET_PSTATE_PAN(1) alternative_else_nop_endif .endm .macro uaccess_enable_not_uao, tmp1, tmp2 + uaccess_ttbr0_enable \tmp1, \tmp2 alternative_if ARM64_ALT_PAN_NOT_UAO SET_PSTATE_PAN(0) alternative_else_nop_endif diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index 2bb17bd556f8..c9ea87198789 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -40,6 +40,9 @@ int main(void) DEFINE(TI_ADDR_LIMIT, offsetof(struct thread_info, addr_limit)); DEFINE(TI_TASK, offsetof(struct thread_info, task)); DEFINE(TI_CPU, offsetof(struct thread_info, cpu)); +#ifdef CONFIG_ARM64_SW_TTBR0_PAN + DEFINE(TSK_TI_TTBR0, offsetof(struct thread_info, ttbr0)); +#endif BLANK(); DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context)); BLANK(); diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index eda7d5915fbb..cdf1dca64133 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -46,6 +46,7 @@ unsigned int compat_elf_hwcap2 __read_mostly; #endif DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS); +EXPORT_SYMBOL(cpu_hwcaps); #define __ARM64_FTR_BITS(SIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \ { \ diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 367e850ece4d..8aa564f58b61 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -187,10 +187,6 @@ alternative_endif eret // return to kernel .endm - .macro get_thread_info, rd - mrs \rd, sp_el0 - .endm - .macro irq_stack_entry mov x19, sp // preserve the original sp diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 0ea9a97467a6..8cfd5ab37743 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -318,14 +318,14 @@ __create_page_tables: * dirty cache lines being evicted. */ mov x0, x25 - add x1, x26, #SWAPPER_DIR_SIZE + add x1, x26, #SWAPPER_DIR_SIZE + RESERVED_TTBR0_SIZE bl __inval_cache_range /* * Clear the idmap and swapper page tables. */ mov x0, x25 - add x6, x26, #SWAPPER_DIR_SIZE + add x6, x26, #SWAPPER_DIR_SIZE + RESERVED_TTBR0_SIZE 1: stp xzr, xzr, [x0], #16 stp xzr, xzr, [x0], #16 stp xzr, xzr, [x0], #16 @@ -404,7 +404,7 @@ __create_page_tables: * tables again to remove any speculatively loaded cache lines. */ mov x0, x25 - add x1, x26, #SWAPPER_DIR_SIZE + add x1, x26, #SWAPPER_DIR_SIZE + RESERVED_TTBR0_SIZE dmb sy bl __inval_cache_range diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 9442a51d3540..7a5228c7abdd 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -194,6 +194,11 @@ SECTIONS swapper_pg_dir = .; . += SWAPPER_DIR_SIZE; +#ifdef CONFIG_ARM64_SW_TTBR0_PAN + reserved_ttbr0 = .; + . += RESERVED_TTBR0_SIZE; +#endif + _end = .; STABS_DEBUG -- 2.34.1