| Message ID | 20240625210933.1620802-6-samuel.holland@sifive.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | riscv: Userspace pointer masking and tagged address ABI | expand |
| Context | Check | Description |
|---|---|---|
| conchuod/vmtest-fixes-PR | fail | merge-conflict |
Hi Samuel, On 25/06/2024 23:09, Samuel Holland wrote: > 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. Would it make sense to have a fast path when S-mode and U-mode PMLENs are equal? > > 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@sifive.com> > --- > > 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; Why don't we use mm->pmlen? I don't see the need to introduce this variable that mirrors what is in mm already but I may be missing something. > + > + /* 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);
Hi Alex, On 2024-08-13 6:35 AM, Alexandre Ghiti wrote: > Hi Samuel, > > On 25/06/2024 23:09, Samuel Holland wrote: >> 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. > > > Would it make sense to have a fast path when S-mode and U-mode PMLENs are equal? I don't think so? Different userspace processes can have different PMLEN values, including PMLEN==0, so it wouldn't be possible to patch out the untagging operation based on PMLEN. (It's already skipped with a static branch if the hardware doesn't support pointer masking). The untagging sequence is only 4 instructions (3 with pmlen in struct thread_info): 746: 41023603 ld a2,1040(tp) current->mm 74a: 46064603 lbu a2,1120(a2) current->mm->context.pmlen 74e: 00c51533 sll a0,a0,a2 752: 40c55533 sra a0,a0,a2 so I'm not sure how to make this faster. >> 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@sifive.com> >> --- >> >> 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; > > > Why don't we use mm->pmlen? I don't see the need to introduce this variable that > mirrors what is in mm already but I may be missing something. Only that caching the value in struct thread_info saves an instruction/cache line load from the pointer chasing. current->mm is likely to be hot anyway, so it probably doesn't make too much difference. I will simplify this in v3. Regards, Samuel >> + >> + /* 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);
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);
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@sifive.com> --- 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(-)