Hi Samuel,
On 25/06/2024 23:09, Samuel Holland wrote:
RISC-V supports pointer masking with a variable number of tag bits
(which is called "PMLEN" in the specification) and which is configured
at the next higher privilege level.
Wire up the PR_SET_TAGGED_ADDR_CTRL and PR_GET_TAGGED_ADDR_CTRL prctls
so userspace can request a lower bound on the number of tag bits and
determine the actual number of tag bits. As with arm64's
PR_TAGGED_ADDR_ENABLE, the pointer masking configuration is
thread-scoped, inherited on clone() and fork() and cleared on execve().
Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
---
Changes in v2:
- Rebase on riscv/linux.git for-next
- Add and use the envcfg_update_bits() helper function
- Inline flush_tagged_addr_state()
arch/riscv/Kconfig | 11 ++++
arch/riscv/include/asm/processor.h | 8 +++
arch/riscv/include/asm/switch_to.h | 11 ++++
arch/riscv/kernel/process.c | 99 ++++++++++++++++++++++++++++++
include/uapi/linux/prctl.h | 3 +
5 files changed, 132 insertions(+)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index b94176e25be1..8f9980f81ea5 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -505,6 +505,17 @@ config RISCV_ISA_C
If you don't know what to do here, say Y.
+config RISCV_ISA_POINTER_MASKING
+ bool "Smmpm, Smnpm, and Ssnpm extensions for pointer masking"
+ depends on 64BIT
+ default y
+ help
+ Add support for the pointer masking extensions (Smmpm, Smnpm,
+ and Ssnpm) when they are detected at boot.
+
+ If this option is disabled, userspace will be unable to use
+ the prctl(PR_{SET,GET}_TAGGED_ADDR_CTRL) API.
+
config RISCV_ISA_SVNAPOT
bool "Svnapot extension support for supervisor mode NAPOT pages"
depends on 64BIT && MMU
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 0838922bd1c8..4f99c85d29ae 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -194,6 +194,14 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
#define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2) riscv_set_icache_flush_ctx(arg1, arg2)
extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread);
+#ifdef CONFIG_RISCV_ISA_POINTER_MASKING
+/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
+long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg);
+long get_tagged_addr_ctrl(struct task_struct *task);
+#define SET_TAGGED_ADDR_CTRL(arg) set_tagged_addr_ctrl(current, arg)
+#define GET_TAGGED_ADDR_CTRL() get_tagged_addr_ctrl(current)
+#endif
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_RISCV_PROCESSOR_H */
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 9685cd85e57c..94e33216b2d9 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -70,6 +70,17 @@ static __always_inline bool has_fpu(void) { return false; }
#define __switch_to_fpu(__prev, __next) do { } while (0)
#endif
+static inline void envcfg_update_bits(struct task_struct *task,
+ unsigned long mask, unsigned long val)
+{
+ unsigned long envcfg;
+
+ envcfg = (task->thread.envcfg & ~mask) | val;
+ task->thread.envcfg = envcfg;
+ if (task == current)
+ csr_write(CSR_ENVCFG, envcfg);
+}
+
static inline void __switch_to_envcfg(struct task_struct *next)
{
asm volatile (ALTERNATIVE("nop", "csrw " __stringify(CSR_ENVCFG) ", %0",
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index e4bc61c4e58a..dec5ccc44697 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -7,6 +7,7 @@
* Copyright (C) 2017 SiFive
*/
+#include <linux/bitfield.h>
#include <linux/cpu.h>
#include <linux/kernel.h>
#include <linux/sched.h>
@@ -171,6 +172,10 @@ void flush_thread(void)
memset(¤t->thread.vstate, 0, sizeof(struct __riscv_v_ext_state));
clear_tsk_thread_flag(current, TIF_RISCV_V_DEFER_RESTORE);
#endif
+#ifdef CONFIG_RISCV_ISA_POINTER_MASKING
+ if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
+ envcfg_update_bits(current, ENVCFG_PMM, ENVCFG_PMM_PMLEN_0);
+#endif
if (IS_ENABLED(CONFIG_RISCV_ISA_POINTER_MASKING) &&
riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
}
void arch_release_task_struct(struct task_struct *tsk)
@@ -233,3 +238,97 @@ void __init arch_task_cache_init(void)
{
riscv_v_setup_ctx_cache();
}
+
+#ifdef CONFIG_RISCV_ISA_POINTER_MASKING
+static bool have_user_pmlen_7;
+static bool have_user_pmlen_16;
+
+long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
+{
+ unsigned long valid_mask = PR_PMLEN_MASK;
+ struct thread_info *ti = task_thread_info(task);
+ unsigned long pmm;
+ u8 pmlen;
+
+ if (is_compat_thread(ti))
+ return -EINVAL;
+
+ if (arg & ~valid_mask)
+ return -EINVAL;
+
+ pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
+ if (pmlen > 16) {
+ return -EINVAL;
+ } else if (pmlen > 7) {
+ if (have_user_pmlen_16)
+ pmlen = 16;
+ else
+ return -EINVAL;
+ } else if (pmlen > 0) {
+ /*
+ * Prefer the smallest PMLEN that satisfies the user's request,
+ * in case choosing a larger PMLEN has a performance impact.
+ */
+ if (have_user_pmlen_7)
+ pmlen = 7;
+ else if (have_user_pmlen_16)
+ pmlen = 16;
+ else
+ return -EINVAL;
+ }
+
+ if (pmlen == 7)
+ pmm = ENVCFG_PMM_PMLEN_7;
+ else if (pmlen == 16)
+ pmm = ENVCFG_PMM_PMLEN_16;
+ else
+ pmm = ENVCFG_PMM_PMLEN_0;
+
+ envcfg_update_bits(task, ENVCFG_PMM, pmm);
+
+ return 0;
+}
+
+long get_tagged_addr_ctrl(struct task_struct *task)
+{
+ struct thread_info *ti = task_thread_info(task);
+ long ret = 0;
+
+ if (is_compat_thread(ti))
+ return -EINVAL;
+
+ switch (task->thread.envcfg & ENVCFG_PMM) {
+ case ENVCFG_PMM_PMLEN_7:
+ ret |= FIELD_PREP(PR_PMLEN_MASK, 7);
+ break;
+ case ENVCFG_PMM_PMLEN_16:
+ ret |= FIELD_PREP(PR_PMLEN_MASK, 16);
+ break;
+ }
No need for the |=
+
+ return ret;
+}
In all the code above, I'd use a macro for 7 and 16, something like
PMLEN[7|16]?
+
+static bool try_to_set_pmm(unsigned long value)
+{
+ csr_set(CSR_ENVCFG, value);
+ return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
+}
+
+static int __init tagged_addr_init(void)
+{
+ if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
+ return 0;
+
+ /*
+ * envcfg.PMM is a WARL field. Detect which values are supported.
+ * Assume the supported PMLEN values are the same on all harts.
+ */
+ csr_clear(CSR_ENVCFG, ENVCFG_PMM);
+ have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
+ have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
Shouldn't this depend on the satp mode? sv57 does not allow 16bits for
the tag.
+
+ return 0;
+}
+core_initcall(tagged_addr_init);
Any reason it's not called from setup_arch()? I see the vector extension
does the same; just wondering if we should not centralize all this early
extensions decisions in setup_arch() (in my Zacas series, I choose the
spinlock implementation in setup_arch()).
+#endif /* CONFIG_RISCV_ISA_POINTER_MASKING */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 35791791a879..6e84c827869b 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -244,6 +244,9 @@ struct prctl_mm_map {
# define PR_MTE_TAG_MASK (0xffffUL << PR_MTE_TAG_SHIFT)
/* Unused; kept only for source compatibility */
# define PR_MTE_TCF_SHIFT 1
+/* RISC-V pointer masking tag length */
+# define PR_PMLEN_SHIFT 24
+# define PR_PMLEN_MASK (0x7fUL << PR_PMLEN_SHIFT)
I don't understand the need for this shift, can't userspace pass the
pmlen value directly without worrying about this?
/* Control reclaim behavior when allocating memory */
#define PR_SET_IO_FLUSHER 57
