When pointer masking is enabled for userspace, the kernel can accept tagged pointers as arguments to some system calls. Allow this by untagging the pointers in access_ok() and the uaccess routines. The uaccess routines must peform untagging in software because U-mode and S-mode have entirely separate pointer masking configurations. In fact, hardware may not even implement pointer masking for S-mode. Since the number of tag bits is variable, untagged_addr_remote() needs to know what PMLEN to use for the remote mm. Therefore, the pointer masking mode must be the same for all threads sharing an mm. Enforce this with a lock flag in the mm context, as x86 does for LAM. The flag gets reset in init_new_context() during fork(), as the new mm is no longer multithreaded. Unlike x86, untagged_addr() gets pmlen from struct thread_info instead of a percpu variable, as this both avoids context switch overhead and loads the value more efficiently. Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx> --- Changes in v2: - Implement untagged_addr_remote() - Restrict PMLEN changes once a process is multithreaded arch/riscv/include/asm/mmu.h | 7 +++ arch/riscv/include/asm/mmu_context.h | 6 +++ arch/riscv/include/asm/thread_info.h | 3 ++ arch/riscv/include/asm/uaccess.h | 58 +++++++++++++++++++++-- arch/riscv/kernel/process.c | 69 +++++++++++++++++++++++++++- 5 files changed, 136 insertions(+), 7 deletions(-) diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h index 947fd60f9051..361a9623f8c8 100644 --- a/arch/riscv/include/asm/mmu.h +++ b/arch/riscv/include/asm/mmu.h @@ -26,8 +26,15 @@ typedef struct { unsigned long exec_fdpic_loadmap; unsigned long interp_fdpic_loadmap; #endif +#ifdef CONFIG_RISCV_ISA_POINTER_MASKING + unsigned long flags; + u8 pmlen; +#endif } mm_context_t; +/* Lock the pointer masking mode because this mm is multithreaded */ +#define MM_CONTEXT_LOCK_PMLEN 0 + #define cntx2asid(cntx) ((cntx) & SATP_ASID_MASK) #define cntx2version(cntx) ((cntx) & ~SATP_ASID_MASK) diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h index 7030837adc1a..62a9f76cf257 100644 --- a/arch/riscv/include/asm/mmu_context.h +++ b/arch/riscv/include/asm/mmu_context.h @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next) { +#ifdef CONFIG_RISCV_ISA_POINTER_MASKING + next->context.pmlen = 0; +#endif switch_mm(prev, next, NULL); } @@ -29,6 +32,9 @@ static inline int init_new_context(struct task_struct *tsk, { #ifdef CONFIG_MMU atomic_long_set(&mm->context.id, 0); +#endif +#ifdef CONFIG_RISCV_ISA_POINTER_MASKING + clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags); #endif return 0; } diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h index 5d473343634b..cd355f8a550f 100644 --- a/arch/riscv/include/asm/thread_info.h +++ b/arch/riscv/include/asm/thread_info.h @@ -60,6 +60,9 @@ struct thread_info { void *scs_base; void *scs_sp; #endif +#ifdef CONFIG_RISCV_ISA_POINTER_MASKING + u8 pmlen; +#endif }; #ifdef CONFIG_SHADOW_CALL_STACK diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h index 72ec1d9bd3f3..153495997bc1 100644 --- a/arch/riscv/include/asm/uaccess.h +++ b/arch/riscv/include/asm/uaccess.h @@ -9,8 +9,56 @@ #define _ASM_RISCV_UACCESS_H #include <asm/asm-extable.h> +#include <asm/cpufeature.h> #include <asm/pgtable.h> /* for TASK_SIZE */ +#ifdef CONFIG_RISCV_ISA_POINTER_MASKING +static inline unsigned long __untagged_addr(unsigned long addr) +{ + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { + u8 pmlen = current->thread_info.pmlen; + + /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ + if (IS_ENABLED(CONFIG_MMU)) + return (long)(addr << pmlen) >> pmlen; + else + return (addr << pmlen) >> pmlen; + } + + return addr; +} + +#define untagged_addr(addr) ({ \ + unsigned long __addr = (__force unsigned long)(addr); \ + (__force __typeof__(addr))__untagged_addr(__addr); \ +}) + +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigned long addr) +{ + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { + u8 pmlen = mm->context.pmlen; + + /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ + if (IS_ENABLED(CONFIG_MMU)) + return (long)(addr << pmlen) >> pmlen; + else + return (addr << pmlen) >> pmlen; + } + + return addr; +} + +#define untagged_addr_remote(mm, addr) ({ \ + unsigned long __addr = (__force unsigned long)(addr); \ + mmap_assert_locked(mm); \ + (__force __typeof__(addr))__untagged_addr_remote(mm, __addr); \ +}) + +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size)) +#else +#define untagged_addr(addr) (addr) +#endif + /* * User space memory access functions */ @@ -130,7 +178,7 @@ do { \ */ #define __get_user(x, ptr) \ ({ \ - const __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ + const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ long __gu_err = 0; \ \ __chk_user_ptr(__gu_ptr); \ @@ -246,7 +294,7 @@ do { \ */ #define __put_user(x, ptr) \ ({ \ - __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ + __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ __typeof__(*__gu_ptr) __val = (x); \ long __pu_err = 0; \ \ @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to, static inline unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n) { - return __asm_copy_from_user(to, from, n); + return __asm_copy_from_user(to, untagged_addr(from), n); } static inline unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n) { - return __asm_copy_to_user(to, from, n); + return __asm_copy_to_user(untagged_addr(to), from, n); } extern long strncpy_from_user(char *dest, const char __user *src, long count); @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n) { might_fault(); return access_ok(to, n) ? - __clear_user(to, n) : n; + __clear_user(untagged_addr(to), n) : n; } #define __get_kernel_nofault(dst, src, type, err_label) \ diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index dec5ccc44697..7bd445dade92 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -173,8 +173,10 @@ void flush_thread(void) clear_tsk_thread_flag(current, TIF_RISCV_V_DEFER_RESTORE); #endif #ifdef CONFIG_RISCV_ISA_POINTER_MASKING - if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { envcfg_update_bits(current, ENVCFG_PMM, ENVCFG_PMM_PMLEN_0); + current->thread_info.pmlen = 0; + } #endif } @@ -204,6 +206,12 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) unsigned long tls = args->tls; struct pt_regs *childregs = task_pt_regs(p); +#ifdef CONFIG_RISCV_ISA_POINTER_MASKING + /* Ensure all threads in this mm have the same pointer masking mode. */ + if (p->mm && (clone_flags & CLONE_VM)) + set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags); +#endif + memset(&p->thread.s, 0, sizeof(p->thread.s)); /* p->thread holds context to be restored by __switch_to() */ @@ -243,10 +251,16 @@ void __init arch_task_cache_init(void) static bool have_user_pmlen_7; static bool have_user_pmlen_16; +/* + * Control the relaxed ABI allowing tagged user addresses into the kernel. + */ +static unsigned int tagged_addr_disabled; + long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) { - unsigned long valid_mask = PR_PMLEN_MASK; + unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE; struct thread_info *ti = task_thread_info(task); + struct mm_struct *mm = task->mm; unsigned long pmm; u8 pmlen; @@ -277,6 +291,14 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) return -EINVAL; } + /* + * Do not allow the enabling of the tagged address ABI if globally + * disabled via sysctl abi.tagged_addr_disabled, if pointer masking + * is disabled for userspace. + */ + if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen)) + return -EINVAL; + if (pmlen == 7) pmm = ENVCFG_PMM_PMLEN_7; else if (pmlen == 16) @@ -284,7 +306,22 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) else pmm = ENVCFG_PMM_PMLEN_0; + if (!(arg & PR_TAGGED_ADDR_ENABLE)) + pmlen = 0; + + if (mmap_write_lock_killable(mm)) + return -EINTR; + + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) { + mmap_write_unlock(mm); + return -EBUSY; + } + envcfg_update_bits(task, ENVCFG_PMM, pmm); + task->mm->context.pmlen = pmlen; + task->thread_info.pmlen = pmlen; + + mmap_write_unlock(mm); return 0; } @@ -297,6 +334,13 @@ long get_tagged_addr_ctrl(struct task_struct *task) if (is_compat_thread(ti)) return -EINVAL; + if (task->thread_info.pmlen) + ret = PR_TAGGED_ADDR_ENABLE; + + /* + * The task's pmlen is only set if the tagged address ABI is enabled, + * so the effective PMLEN must be extracted from envcfg.PMM. + */ switch (task->thread.envcfg & ENVCFG_PMM) { case ENVCFG_PMM_PMLEN_7: ret |= FIELD_PREP(PR_PMLEN_MASK, 7); @@ -315,6 +359,24 @@ static bool try_to_set_pmm(unsigned long value) return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value; } +/* + * Global sysctl to disable the tagged user addresses support. This control + * only prevents the tagged address ABI enabling via prctl() and does not + * disable it for tasks that already opted in to the relaxed ABI. + */ + +static struct ctl_table tagged_addr_sysctl_table[] = { + { + .procname = "tagged_addr_disabled", + .mode = 0644, + .data = &tagged_addr_disabled, + .maxlen = sizeof(int), + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, +}; + static int __init tagged_addr_init(void) { if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) @@ -328,6 +390,9 @@ static int __init tagged_addr_init(void) have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7); have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16); + if (!register_sysctl("abi", tagged_addr_sysctl_table)) + return -EINVAL; + return 0; } core_initcall(tagged_addr_init); -- 2.44.1