[PATCH v5 05/10] riscv: Add support for the tagged address ABI
Samuel Holland
samuel.holland at sifive.com
Wed Oct 16 13:27:46 PDT 2024
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.
Reviewed-by: Charlie Jenkins <charlie at rivosinc.com>
Tested-by: Charlie Jenkins <charlie at rivosinc.com>
Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
---
Changes in v5:
- Document that the RISC-V tagged address ABI is the same as AArch64
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
Documentation/arch/riscv/uabi.rst | 4 ++
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 ++++++++++++++++++++++++++--
5 files changed, 130 insertions(+), 10 deletions(-)
diff --git a/Documentation/arch/riscv/uabi.rst b/Documentation/arch/riscv/uabi.rst
index ddb8359a46ed..243e40062e34 100644
--- a/Documentation/arch/riscv/uabi.rst
+++ b/Documentation/arch/riscv/uabi.rst
@@ -80,3 +80,7 @@ number of mask/tag bits needed by the application. ``PR_PMLEN`` is interpreted
as a lower bound; if the kernel is unable to satisfy the request, the
``PR_SET_TAGGED_ADDR_CTRL`` operation will fail. The actual number of tag bits
is returned in ``PR_PMLEN`` by the ``PR_GET_TAGGED_ADDR_CTRL`` operation.
+
+Additionally, when pointer masking is enabled (``PR_PMLEN`` is greater than 0),
+a tagged address ABI is supported, with the same interface and behavior as
+documented for AArch64 (Documentation/arch/arm64/tagged-address-abi.rst).
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 200d2ed64dfe..58b6482c2bf6 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -213,6 +213,10 @@ 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() */
@@ -258,10 +262,16 @@ 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;
@@ -276,16 +286,41 @@ 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;
}
@@ -298,6 +333,10 @@ 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);
@@ -307,6 +346,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
break;
}
+ if (task->mm->context.pmlen)
+ ret |= PR_TAGGED_ADDR_ENABLE;
+
return ret;
}
@@ -316,6 +358,24 @@ 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))
@@ -329,6 +389,9 @@ 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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