From cbe94edc1c062ba2f31e9d2432a374d17f25a002 Mon Sep 17 00:00:00 2001

From: Russell Currey <ruscur@russell.cc>

Date: Fri, 10 Mar 2023 16:08:34 +1100

Subject: [PATCH] powerpc/mm: Fix false detection of read faults

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Patch-mainline: submitted http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20230310050834.63105-1-ruscur@russell.cc/

References: bsc#1208864

To support detection of read faults with Radix execute-only memory, the

vma_is_accessible() check in access_error() (which checks for PROT_NONE)

was replaced with a check to see if VM_READ was missing, and if so,

returns true to assert the fault was caused by a bad read.

This is incorrect, as it ignores that both VM_WRITE and VM_EXEC imply

read on powerpc, as defined in protection_map[].  This causes mappings

containing VM_WRITE or VM_EXEC without VM_READ to misreport the cause of

page faults, since the MMU is still allowing reads.

Correct this by restoring the original vma_is_accessible() check for

PROT_NONE mappings, and adding a separate check for Radix PROT_EXEC-only

mappings.

Fixes: 395cac7752b9 ("powerpc/mm: Support execute-only memory on the Radix MMU")

Reported-by: Michal Suchánek <msuchanek@suse.de>

Tested-by: Benjamin Gray <bgray@linux.ibm.com>

Signed-off-by: Russell Currey <ruscur@russell.cc>

Acked-by: Michal Suchanek <msuchanek@suse.de>

---

 arch/powerpc/mm/fault.c | 11 ++++++++---

 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c

index 2bef19cc1b98..af46aa88422b 100644

--- a/arch/powerpc/mm/fault.c

+++ b/arch/powerpc/mm/fault.c

@@ -271,11 +271,16 @@ static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma

 	}

 	/*

-	 * Check for a read fault.  This could be caused by a read on an

-	 * inaccessible page (i.e. PROT_NONE), or a Radix MMU execute-only page.

+	 * VM_READ, VM_WRITE and VM_EXEC all imply read permissions, as

+	 * defined in protection_map[].  Read faults can only be caused by

+	 * a PROT_NONE mapping, or with a PROT_EXEC-only mapping on Radix.

 	 */

-	if (unlikely(!(vma->vm_flags & VM_READ)))

+	if (unlikely(!vma_is_accessible(vma)))

 		return true;

+

+	if (unlikely(radix_enabled() && ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)))

+		return true;

+

 	/*

 	 * We should ideally do the vma pkey access check here. But in the

 	 * fault path, handle_mm_fault() also does the same check. To avoid

-- 

2.39.2