From 57f4959bad0a154aeca125b7d38d1d9471a12422 Mon Sep 17 00:00:00 2001 From: James Morse Date: Fri, 5 Feb 2016 14:58:48 +0000 Subject: arm64: kernel: Add support for User Access Override 'User Access Override' is a new ARMv8.2 feature which allows the unprivileged load and store instructions to be overridden to behave in the normal way. This patch converts {get,put}_user() and friends to use ldtr*/sttr* instructions - so that they can only access EL0 memory, then enables UAO when fs==KERNEL_DS so that these functions can access kernel memory. This allows user space's read/write permissions to be checked against the page tables, instead of testing addr [catalin.marinas@arm.com: move uao_thread_switch() above dsb()] Signed-off-by: Catalin Marinas --- arch/arm64/Kconfig | 21 +++++++++++ arch/arm64/include/asm/alternative.h | 72 ++++++++++++++++++++++++++++++++++++ arch/arm64/include/asm/cpufeature.h | 3 +- arch/arm64/include/asm/processor.h | 1 + arch/arm64/include/asm/sysreg.h | 3 ++ arch/arm64/include/asm/thread_info.h | 6 +++ arch/arm64/include/asm/uaccess.h | 44 ++++++++++++++++------ arch/arm64/include/uapi/asm/ptrace.h | 1 + arch/arm64/kernel/cpufeature.c | 11 ++++++ arch/arm64/kernel/process.c | 19 ++++++++++ arch/arm64/lib/clear_user.S | 8 ++-- arch/arm64/lib/copy_from_user.S | 8 ++-- arch/arm64/lib/copy_in_user.S | 16 ++++---- arch/arm64/lib/copy_to_user.S | 8 ++-- arch/arm64/mm/fault.c | 31 +++++++++++++--- 15 files changed, 213 insertions(+), 39 deletions(-) (limited to 'arch') diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index fa51ff0470c1..3d9cab156740 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -756,6 +756,27 @@ config ARM64_LSE_ATOMICS endmenu +config ARM64_UAO + bool "Enable support for User Access Override (UAO)" + default y + help + User Access Override (UAO; part of the ARMv8.2 Extensions) + causes the 'unprivileged' variant of the load/store instructions to + be overriden to be privileged. + + This option changes get_user() and friends to use the 'unprivileged' + variant of the load/store instructions. This ensures that user-space + really did have access to the supplied memory. When addr_limit is + set to kernel memory the UAO bit will be set, allowing privileged + access to kernel memory. + + Choosing this option will cause copy_to_user() et al to use user-space + memory permissions. + + The feature is detected at runtime, the kernel will use the + regular load/store instructions if the cpu does not implement the + feature. + endmenu menu "Boot options" diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index e4962f04201e..a9fc24ec1aa9 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -1,6 +1,8 @@ #ifndef __ASM_ALTERNATIVE_H #define __ASM_ALTERNATIVE_H +#include + #ifndef __ASSEMBLY__ #include @@ -63,6 +65,8 @@ void apply_alternatives(void *start, size_t length); #else +#include + .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len .word \orig_offset - . .word \alt_offset - . @@ -136,6 +140,74 @@ void apply_alternatives(void *start, size_t length); alternative_insn insn1, insn2, cap, IS_ENABLED(cfg) +/* + * Generate the assembly for UAO alternatives with exception table entries. + * This is complicated as there is no post-increment or pair versions of the + * unprivileged instructions, and USER() only works for single instructions. + */ +#ifdef CONFIG_ARM64_UAO + .macro uao_ldp l, reg1, reg2, addr, post_inc + alternative_if_not ARM64_HAS_UAO +8888: ldp \reg1, \reg2, [\addr], \post_inc; +8889: nop; + nop; + alternative_else + ldtr \reg1, [\addr]; + ldtr \reg2, [\addr, #8]; + add \addr, \addr, \post_inc; + alternative_endif + + .section __ex_table,"a"; + .align 3; + .quad 8888b,\l; + .quad 8889b,\l; + .previous; + .endm + + .macro uao_stp l, reg1, reg2, addr, post_inc + alternative_if_not ARM64_HAS_UAO +8888: stp \reg1, \reg2, [\addr], \post_inc; +8889: nop; + nop; + alternative_else + sttr \reg1, [\addr]; + sttr \reg2, [\addr, #8]; + add \addr, \addr, \post_inc; + alternative_endif + + .section __ex_table,"a"; + .align 3; + .quad 8888b,\l; + .quad 8889b,\l; + .previous + .endm + + .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc + alternative_if_not ARM64_HAS_UAO +8888: \inst \reg, [\addr], \post_inc; + nop; + alternative_else + \alt_inst \reg, [\addr]; + add \addr, \addr, \post_inc; + alternative_endif + + .section __ex_table,"a"; + .align 3; + .quad 8888b,\l; + .previous + .endm +#else + .macro uao_ldp l, reg1, reg2, addr, post_inc + USER(\l, ldp \reg1, \reg2, [\addr], \post_inc) + .endm + .macro uao_stp l, reg1, reg2, addr, post_inc + USER(\l, stp \reg1, \reg2, [\addr], \post_inc) + .endm + .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc + USER(\l, \inst \reg, [\addr], \post_inc) + .endm +#endif + #endif /* __ASSEMBLY__ */ /* diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 8131abfabb0a..a5df7cde616b 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -31,8 +31,9 @@ #define ARM64_WORKAROUND_CAVIUM_23154 6 #define ARM64_WORKAROUND_834220 7 #define ARM64_HAS_NO_HW_PREFETCH 8 +#define ARM64_HAS_UAO 9 -#define ARM64_NCAPS 9 +#define ARM64_NCAPS 10 #ifndef __ASSEMBLY__ diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 5bb1d763d17a..cef1cf398356 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -191,5 +191,6 @@ static inline void spin_lock_prefetch(const void *ptr) #endif void cpu_enable_pan(void *__unused); +void cpu_enable_uao(void *__unused); #endif /* __ASM_PROCESSOR_H */ diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index e9c68e636576..1a78d6e2a78b 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -79,9 +79,12 @@ #define SYS_DCZID_EL0 sys_reg(3, 3, 0, 0, 7) #define REG_PSTATE_PAN_IMM sys_reg(0, 0, 4, 0, 4) +#define REG_PSTATE_UAO_IMM sys_reg(0, 0, 4, 0, 3) #define SET_PSTATE_PAN(x) __inst_arm(0xd5000000 | REG_PSTATE_PAN_IMM |\ (!!x)<<8 | 0x1f) +#define SET_PSTATE_UAO(x) __inst_arm(0xd5000000 | REG_PSTATE_UAO_IMM |\ + (!!x)<<8 | 0x1f) /* SCTLR_EL1 */ #define SCTLR_EL1_CP15BEN (0x1 << 5) diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h index abd64bd1f6d9..eba8db6838af 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -85,6 +85,12 @@ static inline struct thread_info *current_thread_info(void) return (struct thread_info *)sp_el0; } +/* Access struct thread_info of another thread */ +static inline struct thread_info *get_thread_info(unsigned long thread_stack) +{ + return (struct thread_info *)(thread_stack & ~(THREAD_SIZE - 1)); +} + #define thread_saved_pc(tsk) \ ((unsigned long)(tsk->thread.cpu_context.pc)) #define thread_saved_sp(tsk) \ diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index b2ede967fe7d..f973bdce8410 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -64,6 +64,16 @@ extern int fixup_exception(struct pt_regs *regs); static inline void set_fs(mm_segment_t fs) { current_thread_info()->addr_limit = fs; + + /* + * Enable/disable UAO so that copy_to_user() etc can access + * kernel memory with the unprivileged instructions. + */ + if (IS_ENABLED(CONFIG_ARM64_UAO) && fs == KERNEL_DS) + asm(ALTERNATIVE("nop", SET_PSTATE_UAO(1), ARM64_HAS_UAO)); + else + asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO, + CONFIG_ARM64_UAO)); } #define segment_eq(a, b) ((a) == (b)) @@ -113,9 +123,10 @@ static inline void set_fs(mm_segment_t fs) * The "__xxx_error" versions set the third argument to -EFAULT if an error * occurs, and leave it unchanged on success. */ -#define __get_user_asm(instr, reg, x, addr, err) \ +#define __get_user_asm(instr, alt_instr, reg, x, addr, err, feature) \ asm volatile( \ - "1: " instr " " reg "1, [%2]\n" \ + "1:"ALTERNATIVE(instr " " reg "1, [%2]\n", \ + alt_instr " " reg "1, [%2]\n", feature) \ "2:\n" \ " .section .fixup, \"ax\"\n" \ " .align 2\n" \ @@ -138,16 +149,20 @@ do { \ CONFIG_ARM64_PAN)); \ switch (sizeof(*(ptr))) { \ case 1: \ - __get_user_asm("ldrb", "%w", __gu_val, (ptr), (err)); \ + __get_user_asm("ldrb", "ldtrb", "%w", __gu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ case 2: \ - __get_user_asm("ldrh", "%w", __gu_val, (ptr), (err)); \ + __get_user_asm("ldrh", "ldtrh", "%w", __gu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ case 4: \ - __get_user_asm("ldr", "%w", __gu_val, (ptr), (err)); \ + __get_user_asm("ldr", "ldtr", "%w", __gu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ case 8: \ - __get_user_asm("ldr", "%", __gu_val, (ptr), (err)); \ + __get_user_asm("ldr", "ldtr", "%", __gu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ default: \ BUILD_BUG(); \ @@ -181,9 +196,10 @@ do { \ ((x) = 0, -EFAULT); \ }) -#define __put_user_asm(instr, reg, x, addr, err) \ +#define __put_user_asm(instr, alt_instr, reg, x, addr, err, feature) \ asm volatile( \ - "1: " instr " " reg "1, [%2]\n" \ + "1:"ALTERNATIVE(instr " " reg "1, [%2]\n", \ + alt_instr " " reg "1, [%2]\n", feature) \ "2:\n" \ " .section .fixup,\"ax\"\n" \ " .align 2\n" \ @@ -205,16 +221,20 @@ do { \ CONFIG_ARM64_PAN)); \ switch (sizeof(*(ptr))) { \ case 1: \ - __put_user_asm("strb", "%w", __pu_val, (ptr), (err)); \ + __put_user_asm("strb", "sttrb", "%w", __pu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ case 2: \ - __put_user_asm("strh", "%w", __pu_val, (ptr), (err)); \ + __put_user_asm("strh", "sttrh", "%w", __pu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ case 4: \ - __put_user_asm("str", "%w", __pu_val, (ptr), (err)); \ + __put_user_asm("str", "sttr", "%w", __pu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ case 8: \ - __put_user_asm("str", "%", __pu_val, (ptr), (err)); \ + __put_user_asm("str", "sttr", "%", __pu_val, (ptr), \ + (err), ARM64_HAS_UAO); \ break; \ default: \ BUILD_BUG(); \ diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h index 208db3df135a..b5c3933ed441 100644 --- a/arch/arm64/include/uapi/asm/ptrace.h +++ b/arch/arm64/include/uapi/asm/ptrace.h @@ -45,6 +45,7 @@ #define PSR_A_BIT 0x00000100 #define PSR_D_BIT 0x00000200 #define PSR_PAN_BIT 0x00400000 +#define PSR_UAO_BIT 0x00800000 #define PSR_Q_BIT 0x08000000 #define PSR_V_BIT 0x10000000 #define PSR_C_BIT 0x20000000 diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 42918c797e8e..ae22edf9d3c9 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -677,6 +677,17 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .capability = ARM64_HAS_NO_HW_PREFETCH, .matches = has_no_hw_prefetch, }, +#ifdef CONFIG_ARM64_UAO + { + .desc = "User Access Override", + .capability = ARM64_HAS_UAO, + .matches = has_cpuid_feature, + .sys_reg = SYS_ID_AA64MMFR2_EL1, + .field_pos = ID_AA64MMFR2_UAO_SHIFT, + .min_field_value = 1, + .enable = cpu_enable_uao, + }, +#endif /* CONFIG_ARM64_UAO */ {}, }; diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 88d742ba19d5..c1ca4ea065d4 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -46,6 +46,7 @@ #include #include +#include #include #include #include @@ -280,6 +281,9 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, } else { memset(childregs, 0, sizeof(struct pt_regs)); childregs->pstate = PSR_MODE_EL1h; + if (IS_ENABLED(CONFIG_ARM64_UAO) && + cpus_have_cap(ARM64_HAS_UAO)) + childregs->pstate |= PSR_UAO_BIT; p->thread.cpu_context.x19 = stack_start; p->thread.cpu_context.x20 = stk_sz; } @@ -308,6 +312,20 @@ static void tls_thread_switch(struct task_struct *next) : : "r" (tpidr), "r" (tpidrro)); } +/* Restore the UAO state depending on next's addr_limit */ +static void uao_thread_switch(struct task_struct *next) +{ + unsigned long next_sp = next->thread.cpu_context.sp; + + if (IS_ENABLED(CONFIG_ARM64_UAO) && + get_thread_info(next_sp)->addr_limit == KERNEL_DS) + asm(ALTERNATIVE("nop", SET_PSTATE_UAO(1), ARM64_HAS_UAO, + CONFIG_ARM64_UAO)); + else + asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO, + CONFIG_ARM64_UAO)); +} + /* * Thread switching. */ @@ -320,6 +338,7 @@ struct task_struct *__switch_to(struct task_struct *prev, tls_thread_switch(next); hw_breakpoint_thread_switch(next); contextidr_thread_switch(next); + uao_thread_switch(next); /* * Complete any pending TLB or cache maintenance on this CPU in case diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S index a9723c71c52b..3f950b677c07 100644 --- a/arch/arm64/lib/clear_user.S +++ b/arch/arm64/lib/clear_user.S @@ -39,20 +39,20 @@ ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_HAS_PAN, \ subs x1, x1, #8 b.mi 2f 1: -USER(9f, str xzr, [x0], #8 ) +uao_user_alternative 9f, str, sttr, xzr, x0, 8 subs x1, x1, #8 b.pl 1b 2: adds x1, x1, #4 b.mi 3f -USER(9f, str wzr, [x0], #4 ) +uao_user_alternative 9f, str, sttr, wzr, x0, 4 sub x1, x1, #4 3: adds x1, x1, #2 b.mi 4f -USER(9f, strh wzr, [x0], #2 ) +uao_user_alternative 9f, strh, sttrh, wzr, x0, 2 sub x1, x1, #2 4: adds x1, x1, #1 b.mi 5f -USER(9f, strb wzr, [x0] ) +uao_user_alternative 9f, strb, sttrb, wzr, x0, 0 5: mov x0, #0 ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_HAS_PAN, \ CONFIG_ARM64_PAN) diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S index 4699cd74f87e..1d982d64f1a7 100644 --- a/arch/arm64/lib/copy_from_user.S +++ b/arch/arm64/lib/copy_from_user.S @@ -34,7 +34,7 @@ */ .macro ldrb1 ptr, regB, val - USER(9998f, ldrb \ptr, [\regB], \val) + uao_user_alternative 9998f, ldrb, ldtrb, \ptr, \regB, \val .endm .macro strb1 ptr, regB, val @@ -42,7 +42,7 @@ .endm .macro ldrh1 ptr, regB, val - USER(9998f, ldrh \ptr, [\regB], \val) + uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val .endm .macro strh1 ptr, regB, val @@ -50,7 +50,7 @@ .endm .macro ldr1 ptr, regB, val - USER(9998f, ldr \ptr, [\regB], \val) + uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val .endm .macro str1 ptr, regB, val @@ -58,7 +58,7 @@ .endm .macro ldp1 ptr, regB, regC, val - USER(9998f, ldp \ptr, \regB, [\regC], \val) + uao_ldp 9998f, \ptr, \regB, \regC, \val .endm .macro stp1 ptr, regB, regC, val diff --git a/arch/arm64/lib/copy_in_user.S b/arch/arm64/lib/copy_in_user.S index 81c8fc93c100..feaad1520dc1 100644 --- a/arch/arm64/lib/copy_in_user.S +++ b/arch/arm64/lib/copy_in_user.S @@ -35,35 +35,35 @@ * x0 - bytes not copied */ .macro ldrb1 ptr, regB, val - USER(9998f, ldrb \ptr, [\regB], \val) + uao_user_alternative 9998f, ldrb, ldtrb, \ptr, \regB, \val .endm .macro strb1 ptr, regB, val - USER(9998f, strb \ptr, [\regB], \val) + uao_user_alternative 9998f, strb, sttrb, \ptr, \regB, \val .endm .macro ldrh1 ptr, regB, val - USER(9998f, ldrh \ptr, [\regB], \val) + uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val .endm .macro strh1 ptr, regB, val - USER(9998f, strh \ptr, [\regB], \val) + uao_user_alternative 9998f, strh, sttrh, \ptr, \regB, \val .endm .macro ldr1 ptr, regB, val - USER(9998f, ldr \ptr, [\regB], \val) + uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val .endm .macro str1 ptr, regB, val - USER(9998f, str \ptr, [\regB], \val) + uao_user_alternative 9998f, str, sttr, \ptr, \regB, \val .endm .macro ldp1 ptr, regB, regC, val - USER(9998f, ldp \ptr, \regB, [\regC], \val) + uao_ldp 9998f, \ptr, \regB, \regC, \val .endm .macro stp1 ptr, regB, regC, val - USER(9998f, stp \ptr, \regB, [\regC], \val) + uao_stp 9998f, \ptr, \regB, \regC, \val .endm end .req x5 diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S index 7512bbbc07ac..2dae2cd2c481 100644 --- a/arch/arm64/lib/copy_to_user.S +++ b/arch/arm64/lib/copy_to_user.S @@ -37,7 +37,7 @@ .endm .macro strb1 ptr, regB, val - USER(9998f, strb \ptr, [\regB], \val) + uao_user_alternative 9998f, strb, sttrb, \ptr, \regB, \val .endm .macro ldrh1 ptr, regB, val @@ -45,7 +45,7 @@ .endm .macro strh1 ptr, regB, val - USER(9998f, strh \ptr, [\regB], \val) + uao_user_alternative 9998f, strh, sttrh, \ptr, \regB, \val .endm .macro ldr1 ptr, regB, val @@ -53,7 +53,7 @@ .endm .macro str1 ptr, regB, val - USER(9998f, str \ptr, [\regB], \val) + uao_user_alternative 9998f, str, sttr, \ptr, \regB, \val .endm .macro ldp1 ptr, regB, regC, val @@ -61,7 +61,7 @@ .endm .macro stp1 ptr, regB, regC, val - USER(9998f, stp \ptr, \regB, [\regC], \val) + uao_stp 9998f, \ptr, \regB, \regC, \val .endm end .req x5 diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 92ddac1e8ca2..820d47353cf0 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -192,6 +192,14 @@ out: return fault; } +static inline int permission_fault(unsigned int esr) +{ + unsigned int ec = (esr & ESR_ELx_EC_MASK) >> ESR_ELx_EC_SHIFT; + unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE; + + return (ec == ESR_ELx_EC_DABT_CUR && fsc_type == ESR_ELx_FSC_PERM); +} + static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, struct pt_regs *regs) { @@ -225,12 +233,10 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, mm_flags |= FAULT_FLAG_WRITE; } - /* - * PAN bit set implies the fault happened in kernel space, but not - * in the arch's user access functions. - */ - if (IS_ENABLED(CONFIG_ARM64_PAN) && (regs->pstate & PSR_PAN_BIT)) - goto no_context; + if (permission_fault(esr) && (addr < USER_DS)) { + if (!search_exception_tables(regs->pc)) + panic("Accessing user space memory outside uaccess.h routines"); + } /* * As per x86, we may deadlock here. However, since the kernel only @@ -561,3 +567,16 @@ void cpu_enable_pan(void *__unused) config_sctlr_el1(SCTLR_EL1_SPAN, 0); } #endif /* CONFIG_ARM64_PAN */ + +#ifdef CONFIG_ARM64_UAO +/* + * Kernel threads have fs=KERNEL_DS by default, and don't need to call + * set_fs(), devtmpfs in particular relies on this behaviour. + * We need to enable the feature at runtime (instead of adding it to + * PSR_MODE_EL1h) as the feature may not be implemented by the cpu. + */ +void cpu_enable_uao(void *__unused) +{ + asm(SET_PSTATE_UAO(1)); +} +#endif /* CONFIG_ARM64_UAO */ -- cgit v1.2.3-59-g8ed1b