From a0509313d5dea0a27a5968f04bd556d05e6349fd Mon Sep 17 00:00:00 2001 From: Anshuman Khandual Date: Mon, 3 Jun 2019 12:11:22 +0530 Subject: [PATCH] arm64/mm: Drop mmap_sem before calling __do_kernel_fault() 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 Cc: Will Deacon Cc: Mark Rutland Cc: James Morse Cc: Andrey Konovalov Signed-off-by: Catalin Marinas --- 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 392386a693fe..2256a1a09f1b 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -504,8 +504,10 @@ retry: */ 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 } -- 2.30.2