Uprobes need more advanced read, push, and pop userspace GCS
functionality. Implement those features using the existing gcsstr()
and copy_from_user().
Its important to note that GCS pages can be read by normal
instructions, but the hardware validates that pages used by GCS
specific operations, have a GCS privilege set. We aren't validating this
in load_user_gcs because it requires stabilizing the VMA over the read
which may fault.
Signed-off-by: Jeremy Linton <jeremy.lin...@arm.com>
Reviewed-by: Catalin Marinas <catalin.mari...@arm.com>
---
arch/arm64/include/asm/gcs.h | 54 ++++++++++++++++++++++++++++++++++++
1 file changed, 54 insertions(+)
diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index e3b360c9dba4..bd9ff1dedcd9 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h
@@ -116,6 +116,47 @@ static inline void put_user_gcs(unsigned long val,
unsigned long __user *addr,
uaccess_ttbr0_disable();
}
+static inline void push_user_gcs(unsigned long val, int *err)
+{
+ u64 gcspr = read_sysreg_s(SYS_GCSPR_EL0);
+
+ gcspr -= sizeof(u64);
+ put_user_gcs(val, (unsigned long __user *)gcspr, err);
+ if (!*err)
+ write_sysreg_s(gcspr, SYS_GCSPR_EL0);
+}
+
+/*
+ * Unlike put/push_user_gcs() above, get/pop_user_gsc() doesn't
+ * validate the GCS permission is set on the page being read. This
+ * differs from how the hardware works when it consumes data stored at
+ * GCSPR. Callers should assure this is acceptable.
+ */
+static inline u64 get_user_gcs(unsigned long __user *addr, int *err)
+{
+ unsigned long ret;
+ u64 load = 0;
+
+ /* Ensure previous GCS operation are visible before we read the page */
+ gcsb_dsync();
+ ret = copy_from_user(&load, addr, sizeof(load));
+ if (ret != 0)
+ *err = ret;
+ return load;
+}
+
+static inline u64 pop_user_gcs(int *err)
+{
+ u64 gcspr = read_sysreg_s(SYS_GCSPR_EL0);
+ u64 read_val;
+
+ read_val = get_user_gcs((unsigned long __user *)gcspr, err);
+ if (!*err)
+ write_sysreg_s(gcspr + sizeof(u64), SYS_GCSPR_EL0);
+
+ return read_val;
+}
+
#else
static inline bool task_gcs_el0_enabled(struct task_struct *task)
@@ -126,6 +167,10 @@ static inline bool task_gcs_el0_enabled(struct task_struct
*task)
static inline void gcs_set_el0_mode(struct task_struct *task) { }
static inline void gcs_free(struct task_struct *task) { }
static inline void gcs_preserve_current_state(void) { }
+static inline void put_user_gcs(unsigned long val, unsigned long __user *addr,
+ int *err) { }
+static inline void push_user_gcs(unsigned long val, int *err) { }
+
static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
const struct
kernel_clone_args *args)
{
@@ -136,6 +181,15 @@ static inline int gcs_check_locked(struct task_struct
*task,
{
return 0;
}
+static inline u64 load_user_gcs(unsigned long __user *addr, int *err)
+{
+ *err = -EFAULT;
+ return 0;
+}
+static inline u64 pop_user_gcs(int *err)
+{
+ return 0;
+}
#endif
--
2.50.1
