[RFC PATCH 04/16] arm64: Introduce por_set_pkey_perms() helper

Kevin Brodsky
2024-12-06T10:13:25Z

Introduce a helper that sets the permissions of a given pkey
(POIndex) in the POR_ELx format, and make use of it in
arch_set_user_pkey_access().

Also ensure that <asm/sysreg.h> is included in asm/por.h to provide
the POE_* definitions.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
arch/arm64/include/asm/por.h | 9 +++++++++
arch/arm64/mm/mmu.c | 28 ++++++++++------------------
2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/include/asm/por.h b/arch/arm64/include/asm/por.h
index e06e9f473675..7f0d73980cce 100644
--- a/arch/arm64/include/asm/por.h
+++ b/arch/arm64/include/asm/por.h
@@ -6,6 +6,8 @@
#ifndef _ASM_ARM64_POR_H
#define _ASM_ARM64_POR_H

+#include <asm/sysreg.h>
+
#define POR_BITS_PER_PKEY 4
#define POR_ELx_IDX(por_elx, idx) (((por_elx) >> ((idx) * POR_BITS_PER_PKEY)) & 0xf)

@@ -30,4 +32,11 @@ static inline bool por_elx_allows_exec(u64 por, u8 pkey)
return perm & POE_X;
}

+static inline u64 por_set_pkey_perms(u64 por, u8 pkey, u64 perms)
+{
+ u64 shift = pkey * POR_BITS_PER_PKEY;
+
+ return (por & ~(POE_MASK << shift)) | (perms << shift);
+}
+
#endif /* _ASM_ARM64_POR_H */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index e2739b69e11b..20e0390ee382 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1554,9 +1554,8 @@ void __cpu_replace_ttbr1(pgd_t *pgdp, bool cnp)
#ifdef CONFIG_ARCH_HAS_PKEYS
int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val)
{
- u64 new_por = POE_RXW;
- u64 old_por;
- u64 pkey_shift;
+ u64 new_perms;
+ u64 por;

if (!system_supports_poe())
return -ENOSPC;
@@ -1570,26 +1569,19 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long i
return -EINVAL;

/* Set the bits we need in POR: */
- new_por = POE_RXW;
+ new_perms = POE_RXW;
if (init_val & PKEY_DISABLE_WRITE)
- new_por &= ~POE_W;
+ new_perms &= ~POE_W;
if (init_val & PKEY_DISABLE_ACCESS)
- new_por &= ~POE_RW;
+ new_perms &= ~POE_RW;
if (init_val & PKEY_DISABLE_READ)
- new_por &= ~POE_R;
+ new_perms &= ~POE_R;
if (init_val & PKEY_DISABLE_EXECUTE)
- new_por &= ~POE_X;
+ new_perms &= ~POE_X;

- /* Shift the bits in to the correct place in POR for pkey: */
- pkey_shift = pkey * POR_BITS_PER_PKEY;
- new_por <<= pkey_shift;
-
- /* Get old POR and mask off any old bits in place: */
- old_por = read_sysreg_s(SYS_POR_EL0);
- old_por &= ~(POE_MASK << pkey_shift);
-
- /* Write old part along with new part: */
- write_sysreg_s(old_por | new_por, SYS_POR_EL0);
+ por = read_sysreg_s(SYS_POR_EL0);
+ por = por_set_pkey_perms(por, pkey, new_perms);
+ write_sysreg_s(por, SYS_POR_EL0);

return 0;
}
--
2.47.0