[PATCH 2/6] PKEY: Add arch_check_pkey_enforce_api()

jeffxu
2023-05-15T13:07:01Z

From: Jeff Xu <jeffxu@google.com>

This patch adds an architecture-independent function,
arch_check_pkey_enforce_api(), that checks whether the calling thread
has write access to the PKRU for a given range of memory. If the
memory range is protected by PKEY_ENFORCE_API, then the thread must
have write access to the PKRU in order to make changes to the memory
mapping (such as mprotect/munmap).

This function is used by the kernel to enforce the
PKEY_ENFORCE_API flag.

Signed-off-by: Jeff Xu<jeffxu@google.com>
---
arch/powerpc/include/asm/pkeys.h | 8 +++++
arch/x86/include/asm/pkeys.h | 50 ++++++++++++++++++++++++++++++++
include/linux/pkeys.h | 9 ++++++
3 files changed, 67 insertions(+)

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 943333ac0fee..24c481e5e95b 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -177,5 +177,13 @@ static inline bool arch_check_pkey_alloc_flags(unsigned long flags)
return true;
}

+static inline int arch_check_pkey_enforce_api(struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
+{
+ /* Allow by default */
+ return 0;
+}
+
extern void pkey_mm_init(struct mm_struct *mm);
#endif /*_ASM_POWERPC_KEYS_H */
diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index ecadf04a8251..8b94ffc4ca32 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -161,4 +161,54 @@ static inline bool arch_check_pkey_alloc_flags(unsigned long flags)

return true;
}
+
+static inline int __arch_check_vma_pkey_for_write(struct vm_area_struct *vma)
+{
+ int pkey = vma_pkey(vma);
+
+ if (mm_pkey_enforce_api(vma->vm_mm, pkey)) {
+ if (!__pkru_allows_write(read_pkru(), pkey))
+ return -EACCES;
+ }
+
+ return 0;
+}
+
+/*
+ * arch_check_pkey_enforce_api is used by the kernel to enforce
+ * PKEY_ENFORCE_API flag.
+ * It checks whether the calling thread has write access to the PKRU
+ * for a given range of memory. If the memory range is protected by
+ * PKEY_ENFORCE_API, then the thread must have write access to the
+ * PKRU in order to make changes to the memory mapping, such as
+ * mprotect/munmap.
+ */
+static inline int arch_check_pkey_enforce_api(struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
+{
+ int error;
+ struct vm_area_struct *vma;
+
+ if (!arch_pkeys_enabled())
+ return 0;
+
+ while (true) {
+ vma = find_vma_intersection(mm, start, end);
+ if (!vma)
+ break;
+
+ error = __arch_check_vma_pkey_for_write(vma);
+ if (error)
+ return error;
+
+ if (vma->vm_end >= end)
+ break;
+
+ start = vma->vm_end;
+ }
+
+ return 0;
+}
+
#endif /*_ASM_X86_PKEYS_H */
diff --git a/include/linux/pkeys.h b/include/linux/pkeys.h
index 81a482c3e051..7b00689e1c24 100644
--- a/include/linux/pkeys.h
+++ b/include/linux/pkeys.h
@@ -53,6 +53,15 @@ static inline bool arch_check_pkey_alloc_flags(unsigned long flags)
return false;
return true;
}
+
+static inline int arch_check_pkey_enforce_api(struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
+{
+ // Allow by default.
+ return 0;
+}
+
#endif /* ! CONFIG_ARCH_HAS_PKEYS */

#endif /* _LINUX_PKEYS_H */
--
2.40.1.606.ga4b1b128d6-goog