[PATCH 02/10] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support

ira.weiny
2020-10-22T22:27:51Z

Define a helper, update_pkey_val(), which will be used to support both
Protection Key User (PKU) and the new Protection Key for Supervisor
(PKS) in subsequent patches.

Co-developed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes from RFC V3:
Per Dave Hansen
Update and add comments per Dave's review
Per Peter
Correct attribution
---
arch/x86/include/asm/pkeys.h | 2 ++
arch/x86/kernel/fpu/xstate.c | 22 ++++------------------
arch/x86/mm/pkeys.c | 23 +++++++++++++++++++++++
3 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index f9feba80894b..4526245b03e5 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -136,4 +136,6 @@ static inline int vma_pkey(struct vm_area_struct *vma)
return (vma->vm_flags & vma_pkey_mask) >> VM_PKEY_SHIFT;
}

+u32 update_pkey_val(u32 pk_reg, int pkey, unsigned int flags);
+
#endif /*_ASM_X86_PKEYS_H */
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index a99afc70cc0a..a3bca3211eba 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -994,9 +994,7 @@ const void *get_xsave_field_ptr(int xfeature_nr)
int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
unsigned long init_val)
{
- u32 old_pkru;
- int pkey_shift = (pkey * PKR_BITS_PER_PKEY);
- u32 new_pkru_bits = 0;
+ u32 pkru;

/*
* This check implies XSAVE support. OSPKE only gets
@@ -1012,21 +1010,9 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
*/
WARN_ON_ONCE(pkey >= arch_max_pkey());

- /* Set the bits we need in PKRU: */
- if (init_val & PKEY_DISABLE_ACCESS)
- new_pkru_bits |= PKR_AD_BIT;
- if (init_val & PKEY_DISABLE_WRITE)
- new_pkru_bits |= PKR_WD_BIT;
-
- /* Shift the bits in to the correct place in PKRU for pkey: */
- new_pkru_bits <<= pkey_shift;
-
- /* Get old PKRU and mask off any old bits in place: */
- old_pkru = read_pkru();
- old_pkru &= ~((PKR_AD_BIT|PKR_WD_BIT) << pkey_shift);
-
- /* Write old part along with new part: */
- write_pkru(old_pkru | new_pkru_bits);
+ pkru = read_pkru();
+ pkru = update_pkey_val(pkru, pkey, init_val);
+ write_pkru(pkru);

return 0;
}
diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index f5efb4007e74..d1dfe743e79f 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -208,3 +208,26 @@ static __init int setup_init_pkru(char *opt)
return 1;
}
__setup("init_pkru=", setup_init_pkru);
+
+/*
+ * Replace disable bits for @pkey with values from @flags
+ *
+ * Kernel users use the same flags as user space:
+ * PKEY_DISABLE_ACCESS
+ * PKEY_DISABLE_WRITE
+ */
+u32 update_pkey_val(u32 pk_reg, int pkey, unsigned int flags)
+{
+ int pkey_shift = pkey * PKR_BITS_PER_PKEY;
+
+ /* Mask out old bit values */
+ pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);
+
+ /* Or in new values */
+ if (flags & PKEY_DISABLE_ACCESS)
+ pk_reg |= PKR_AD_BIT << pkey_shift;
+ if (flags & PKEY_DISABLE_WRITE)
+ pk_reg |= PKR_WD_BIT << pkey_shift;
+
+ return pk_reg;
+}
--
2.28.0.rc0.12.gb6a658bd00c9