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