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Shutemov" Subject: Re: [PATCH v4 05/10] riscv: Add support for the tagged address ABI Message-ID: References: <20240829010151.2813377-1-samuel.holland@sifive.com> <20240829010151.2813377-6-samuel.holland@sifive.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240829010151.2813377-6-samuel.holland@sifive.com> On Wed, Aug 28, 2024 at 06:01:27PM -0700, 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 > --- Not necessary, but what do you think about adding riscv to include/uapi/linux/prctl.h: /* Tagged user address controls for arm64 */ #define PR_SET_TAGGED_ADDR_CTRL 55 #define PR_GET_TAGGED_ADDR_CTRL 56 # define PR_TAGGED_ADDR_ENABLE (1UL << 0) Also looks like this last line should probably be under SET rather than GET. Reviewed-by: Charlie Jenkins Tested-by: Charlie Jenkins > > Changes in v4: > - Combine __untagged_addr() and __untagged_addr_remote() > > 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 | 43 ++++++++++++++-- > arch/riscv/kernel/process.c | 73 ++++++++++++++++++++++++++-- > 4 files changed, 126 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 > > #endif /* _ASM_RISCV_MMU_CONTEXT_H */ > diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h > index 72ec1d9bd3f3..fee56b0c8058 100644 > --- a/arch/riscv/include/asm/uaccess.h > +++ b/arch/riscv/include/asm/uaccess.h > @@ -9,8 +9,41 @@ > #define _ASM_RISCV_UACCESS_H > > #include > +#include > #include /* for TASK_SIZE */ > > +#ifdef CONFIG_RISCV_ISA_SUPM > +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(addr) ({ \ > + unsigned long __addr = (__force unsigned long)(addr); \ > + (__force __typeof__(addr))__untagged_addr_remote(current->mm, __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 +163,7 @@ 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 +279,7 @@ 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 +326,13 @@ 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 +347,7 @@ 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 f39221ab5ddd..6e9c84a41c29 100644 > --- a/arch/riscv/kernel/process.c > +++ b/arch/riscv/kernel/process.c > @@ -204,6 +204,10 @@ 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() */ > @@ -249,10 +253,16 @@ 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; > > @@ -267,16 +277,41 @@ 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; > } > @@ -289,6 +324,10 @@ 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); > @@ -298,6 +337,9 @@ long get_tagged_addr_ctrl(struct task_struct *task) > break; > } > > + if (task->mm->context.pmlen) > + ret |= PR_TAGGED_ADDR_ENABLE; > + > return ret; > } > > @@ -307,6 +349,24 @@ 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)) > @@ -320,6 +380,9 @@ 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); > -- > 2.45.1 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv