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Subject[PATCH] arm64: print a fault message when attempting to write RO memory
Date
If a page is marked read only we should print out that fact,
instead of printing out that there was a page fault. Right now we
get a cryptic error message that something went wrong with an
unhandled fault, but we don't evaluate the esr to figure out that
it was a read/write permission fault.

Instead of seeing:

Unable to handle kernel paging request at virtual address ffff000008e460d8
pgd = ffff800003504000
[ffff000008e460d8] *pgd=0000000083473003, *pud=0000000083503003, *pmd=0000000000000000
Internal error: Oops: 9600004f [#1] PREEMPT SMP

we'll see:

Internal error: Attempting to write read-only memory: 9600004f [#1] PREEMPT SMP

Cc: Laura Abbott <labbott@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
---
arch/arm64/mm/fault.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 156169c6981b..752507fa80ec 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -331,6 +331,11 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,

if (!search_exception_tables(regs->pc))
die("Accessing user space memory outside uaccess.h routines", regs, esr);
+ } else if (is_permission_fault(esr, regs)) {
+ if (esr & ESR_ELx_WNR)
+ die("Attempting to write read-only memory", regs, esr);
+ else
+ die("Attempting to read unreadable memory", regs, esr);
}

/*
--
2.10.0.297.gf6727b0
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