linux-kernel - [PATCH v10 19/27] powerpc: Handle exceptions caused by pkey violation

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Date:   Thu, 18 Jan 2018 17:50:40 -0800
From:   Ram Pai <linuxram@...ibm.com>
To:     mpe@...erman.id.au, mingo@...hat.com, akpm@...ux-foundation.org,
        corbet@....net, arnd@...db.de
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com,
        linuxram@...ibm.com
Subject: [PATCH v10 19/27] powerpc: Handle exceptions caused by pkey violation

Handle Data and  Instruction exceptions caused by memory
protection-key.

The CPU will detect the key fault if the HPTE is already
programmed with the key.

However if the HPTE is not  hashed, a key fault will not
be detected by the hardware. The software will detect
pkey violation in such a case.

Signed-off-by: Ram Pai <linuxram@...ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
---
 arch/powerpc/include/asm/reg.h       |    1 -
 arch/powerpc/kernel/exceptions-64s.S |    2 +-
 arch/powerpc/mm/fault.c              |   22 ++++++++++++++++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index b779f3c..ffc9990 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -312,7 +312,6 @@
 				 DSISR_BAD_EXT_CTRL)
 #define	  DSISR_BAD_FAULT_64S	(DSISR_BAD_FAULT_32S	| \
 				 DSISR_ATTR_CONFLICT	| \
-				 DSISR_KEYFAULT		| \
 				 DSISR_UNSUPP_MMU	| \
 				 DSISR_PRTABLE_FAULT	| \
 				 DSISR_ICSWX_NO_CT	| \
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index e441b46..804e804 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1521,7 +1521,7 @@ USE_TEXT_SECTION()
 	.balign	IFETCH_ALIGN_BYTES
 do_hash_page:
 #ifdef CONFIG_PPC_BOOK3S_64
-	lis	r0,(DSISR_BAD_FAULT_64S|DSISR_DABRMATCH)@h
+	lis	r0,(DSISR_BAD_FAULT_64S | DSISR_DABRMATCH | DSISR_KEYFAULT)@h
 	ori	r0,r0,DSISR_BAD_FAULT_64S@l
 	and.	r0,r4,r0		/* weird error? */
 	bne-	handle_page_fault	/* if not, try to insert a HPTE */
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 4797d08..943a91e 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -427,6 +427,11 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
 
+	if (error_code & DSISR_KEYFAULT) {
+		_exception(SIGSEGV, regs, SEGV_PKUERR, address);
+		return 0;
+	}
+
 	/*
 	 * We want to do this outside mmap_sem, because reading code around nip
 	 * can result in fault, which will cause a deadlock when called with
@@ -498,6 +503,23 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 	 * the fault.
 	 */
 	fault = handle_mm_fault(vma, address, flags);
+
+#ifdef CONFIG_PPC_MEM_KEYS
+	/*
+	 * if the HPTE is not hashed, hardware will not detect
+	 * a key fault. Lets check if we failed because of a
+	 * software detected key fault.
+	 */
+	if (unlikely(fault & VM_FAULT_SIGSEGV) &&
+		!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+			is_exec, 0)) {
+		int pkey = vma_pkey(vma);
+
+		if (likely(pkey))
+			return __bad_area(regs, address, SEGV_PKUERR);
+	}
+#endif /* CONFIG_PPC_MEM_KEYS */
+
 	major |= fault & VM_FAULT_MAJOR;
 
 	/*
-- 
1.7.1