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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: On Fri, Sep 13, 2024 at 09:57:05PM -0500, Samuel Holland wrote: > Hi Charlie, > > On 2024-09-12 9:45 PM, Charlie Jenkins wrote: > > 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) > > Yes, I'll add this in v5. > > > Also looks like this last line should probably be under SET rather than > > GET. > > The same bit fields are used for both prctl() functions, so I think the current > grouping is okay (compare PR_RISCV_V_GET_CONTROL). Oh perfect, I had missed that when I briefly looked. > > Regards, > Samuel > > > 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 >