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arm64: uaccess: Add additional userspace GCS accessors

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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.linton@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
[will: Add '__force' to gcspr cast in pop_user_gcs()]
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Jeremy Linton 2025-08-24 22:34:17 -05:00 • committed by Will Deacon
parent ea920b50ac
commit 9cd2a7f118
1 changed files with 54 additions and 0 deletions
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54
arch/arm64/include/asm/gcs.h
View file

@ -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 ensure 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((__force 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 get_user_gcs(unsigned long __user *addr, int *err)
{
*err = -EFAULT;
return 0;
}
static inline u64 pop_user_gcs(int *err)
{
return 0;
}
#endif