linux-kernel - [RFC v6 27/62] powerpc: helper to validate key-access permissions of a pte

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Date:   Sat, 15 Jul 2017 20:56:29 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, dave.hansen@...el.com, hbabu@...ibm.com,
        linuxram@...ibm.com, arnd@...db.de, akpm@...ux-foundation.org,
        corbet@....net, mingo@...hat.com, mhocko@...nel.org
Subject: [RFC v6 27/62] powerpc: helper to validate key-access permissions of a pte

helper function that checks if the read/write/execute is allowed
on the pte.

Signed-off-by: Ram Pai <linuxram@...ibm.com>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h |    4 +++
 arch/powerpc/include/asm/pkeys.h             |   12 +++++++++
 arch/powerpc/mm/pkeys.c                      |   33 ++++++++++++++++++++++++++
 3 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 30d7f55..0056e58 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -472,6 +472,10 @@ static inline void write_uamor(u64 value)
 	mtspr(SPRN_UAMOR, value);
 }
 
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+extern bool arch_pte_access_permitted(u64 pte, bool write, bool execute);
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+
 #define __HAVE_ARCH_PTEP_GET_AND_CLEAR
 static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
 				       unsigned long addr, pte_t *ptep)
diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index bbb5d85..7a9aade 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -53,6 +53,18 @@ static inline u64 pte_to_hpte_pkey_bits(u64 pteflags)
 		((pteflags & H_PAGE_PKEY_BIT4) ? HPTE_R_KEY_BIT4 : 0x0UL));
 }
 
+static inline u16 pte_to_pkey_bits(u64 pteflags)
+{
+	if (!pkey_inited)
+		return 0x0UL;
+
+	return (((pteflags & H_PAGE_PKEY_BIT0) ? 0x10 : 0x0UL) |
+		((pteflags & H_PAGE_PKEY_BIT1) ? 0x8 : 0x0UL) |
+		((pteflags & H_PAGE_PKEY_BIT2) ? 0x4 : 0x0UL) |
+		((pteflags & H_PAGE_PKEY_BIT3) ? 0x2 : 0x0UL) |
+		((pteflags & H_PAGE_PKEY_BIT4) ? 0x1 : 0x0UL));
+}
+
 static inline int vma_pkey(struct vm_area_struct *vma)
 {
 	if (!pkey_inited)
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 403f5ae..1794e17 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -201,3 +201,36 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
 	 */
 	return vma_pkey(vma);
 }
+
+static bool pkey_access_permitted(int pkey, bool write, bool execute)
+{
+	int pkey_shift;
+	u64 amr;
+
+	if (!pkey)
+		return true;
+
+	pkey_shift = pkeyshift(pkey);
+	if (!(read_uamor() & (0x3UL << pkey_shift)))
+		return true;
+
+	if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
+		return true;
+
+	if (!write) {
+		amr = read_amr();
+		if (!(amr & (AMR_RD_BIT << pkey_shift)))
+			return true;
+	}
+
+	amr = read_amr(); /* delay reading amr uptil absolutely needed */
+	return (write && !(amr & (AMR_WR_BIT << pkey_shift)));
+}
+
+bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
+{
+	if (!pkey_inited)
+		return true;
+	return pkey_access_permitted(pte_to_pkey_bits(pte),
+			write, execute);
+}
-- 
1.7.1