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From: Anshuman Khandual <anshuman.khandual@arm.com>
To: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	James Morse <james.morse@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH 1/4] arm64/mm: Drop mmap_sem before calling __do_kernel_fault()
Date: Wed, 29 May 2019 18:04:42 +0530	[thread overview]
Message-ID: <1559133285-27986-2-git-send-email-anshuman.khandual@arm.com> (raw)
In-Reply-To: <1559133285-27986-1-git-send-email-anshuman.khandual@arm.com>

There is an inconsistency between down_read_trylock() success and failure
paths while dealing with kernel access for non exception table areas where
it calls __do_kernel_fault(). In case of failure it just bails out without
holding mmap_sem but when it succeeds it does so while holding mmap_sem.
Fix this inconsistency by just dropping mmap_sem in success path as well.

__do_kernel_fault() calls die_kernel_fault() which then calls show_pte().
show_pte() in this path might become bit more unreliable without holding
mmap_sem. But there are already instances [1] in do_page_fault() where
die_kernel_fault() gets called without holding mmap_sem. show_pte() can
be made more robust independently but in a later patch.

[1] Conditional block for (is_ttbr0_addr && is_el1_permission_fault)

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/mm/fault.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index a30818e..dc1cf32 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -503,8 +503,10 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 		 */
 		might_sleep();
 #ifdef CONFIG_DEBUG_VM
-		if (!user_mode(regs) && !search_exception_tables(regs->pc))
+		if (!user_mode(regs) && !search_exception_tables(regs->pc)) {
+			up_read(&mm->mmap_sem);
 			goto no_context;
+		}
 #endif
 	}
 
-- 
2.7.4


  reply	other threads:[~2019-05-29 12:34 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 12:34 [PATCH 0/4] arm64/mm: Fixes and cleanups for do_page_fault() Anshuman Khandual
2019-05-29 12:34 ` Anshuman Khandual [this message]
2019-05-29 12:34 ` [PATCH 2/4] arm64/mm: Drop task_struct argument from __do_page_fault() Anshuman Khandual
2019-05-29 12:34 ` [PATCH 3/4] arm64/mm: Consolidate page fault information capture Anshuman Khandual
2019-05-29 14:53   ` Mark Rutland
2019-05-31  9:10     ` Anshuman Khandual
2019-05-29 12:34 ` [PATCH 4/4] arm64/mm: Drop vm_fault_t argument from __do_page_fault() Anshuman Khandual
2019-05-29 15:11   ` Mark Rutland
2019-05-31  9:05     ` Anshuman Khandual
2019-05-30  6:34   ` Christoph Hellwig
2019-05-31  8:55     ` Anshuman Khandual
2019-05-29 12:41 ` [PATCH 0/4] arm64/mm: Fixes and cleanups for do_page_fault() Will Deacon
2019-05-29 12:59   ` Anshuman Khandual

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