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 <samuel.holland@xxxxxxxxxx>
> ---
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 <charlie@xxxxxxxxxxxx>
Tested-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
>
> 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 <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..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 <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_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
>
>
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