Hi Alex, On 2024-08-14 10:10 AM, Alexandre Ghiti wrote: > On 14/08/2024 10:13, 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. >> >> 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. >> >> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx> >> --- >> >> Changes in v3: >> - Use IS_ENABLED instead of #ifdef when possible >> - Implement mm_untag_mask() >> - Remove pmlen from struct thread_info (now only in mm_context_t) >> >> 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 | 13 +++++ >> arch/riscv/include/asm/uaccess.h | 58 ++++++++++++++++++++-- >> arch/riscv/kernel/process.c | 73 ++++++++++++++++++++++++++-- >> 4 files changed, 141 insertions(+), 10 deletions(-) >> >> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h >> index c9e03e9da3dc..1cc90465d75b 100644 >> --- a/arch/riscv/include/asm/mmu.h >> +++ b/arch/riscv/include/asm/mmu.h >> @@ -25,9 +25,16 @@ typedef struct { >> #ifdef CONFIG_BINFMT_ELF_FDPIC >> unsigned long exec_fdpic_loadmap; >> unsigned long interp_fdpic_loadmap; >> +#endif >> + unsigned long flags; >> +#ifdef CONFIG_RISCV_ISA_SUPM >> + 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..8c4bc49a3a0f 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_SUPM >> + next->context.pmlen = 0; >> +#endif >> switch_mm(prev, next, NULL); >> } >> @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk, >> #ifdef CONFIG_MMU >> atomic_long_set(&mm->context.id, 0); >> #endif >> + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM)) >> + clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags); >> return 0; >> } >> DECLARE_STATIC_KEY_FALSE(use_asid_allocator); >> +#ifdef CONFIG_RISCV_ISA_SUPM >> +#define mm_untag_mask mm_untag_mask >> +static inline unsigned long mm_untag_mask(struct mm_struct *mm) >> +{ >> + return -1UL >> mm->context.pmlen; >> +} >> +#endif >> + >> #include <asm-generic/mmu_context.h> >> #endif /* _ASM_RISCV_MMU_CONTEXT_H */ >> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h >> index 72ec1d9bd3f3..6416559232a2 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_SUPM >> +static inline unsigned long __untagged_addr(unsigned long addr) >> +{ >> + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { >> + u8 pmlen = current->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(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; >> +} > > > I should have mentioned that in v2: now that you removed the thread_info pmlen > field, __untagged_addr_remote() and __untagged_addr() are almost the same, can > you merge them? I can merge them, but this places the load of current->mm outside the static branch. If you think that is okay, then I'll merge them for v4. Regards, Samuel >> + >> +#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 1280a7c4a412..f4d8e5c3bb84 100644 >> --- a/arch/riscv/kernel/process.c >> +++ b/arch/riscv/kernel/process.c >> @@ -203,6 +203,10 @@ 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); >> + /* Ensure all threads in this mm have the same pointer masking mode. */ >> + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM)) >> + set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags); >> + >> memset(&p->thread.s, 0, sizeof(p->thread.s)); >> /* p->thread holds context to be restored by __switch_to() */ >> @@ -248,10 +252,16 @@ enum { >> 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; >> @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, >> unsigned long arg) >> * in case choosing a larger PMLEN has a performance impact. >> */ >> pmlen = FIELD_GET(PR_PMLEN_MASK, arg); >> - if (pmlen == PMLEN_0) >> + if (pmlen == PMLEN_0) { >> pmm = ENVCFG_PMM_PMLEN_0; >> - else if (pmlen <= PMLEN_7 && have_user_pmlen_7) >> + } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) { >> + pmlen = PMLEN_7; >> pmm = ENVCFG_PMM_PMLEN_7; >> - else if (pmlen <= PMLEN_16 && have_user_pmlen_16) >> + } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) { >> + pmlen = PMLEN_16; >> pmm = ENVCFG_PMM_PMLEN_16; >> - else >> + } else { >> 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 (!(arg & PR_TAGGED_ADDR_ENABLE)) >> + pmlen = 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); >> + mm->context.pmlen = pmlen; >> + >> + mmap_write_unlock(mm); >> return 0; >> } >> @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task) >> if (is_compat_thread(ti)) >> return -EINVAL; >> + /* >> + * The mm context's pmlen is set only when 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, PMLEN_7); >> @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task) >> break; >> } >> + if (task->mm->context.pmlen) >> + ret |= PR_TAGGED_ADDR_ENABLE; >> + >> return ret; >> } >> @@ -306,6 +348,24 @@ 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)) >> @@ -319,6 +379,9 @@ 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);