From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Mon, 5 Mar 2018 10:31:15 +0000 Subject: [RFC PATCH] arm64: fault: Don't populate ESR context for user fault on kernel VA Message-ID: <1520245875-32527-1-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org User faults on kernel addresses are a good sign that the faulting task is either up to no good or is in deep trouble. In such situations, exposing the optional ESR context on the sigframe as part of the delivered signal is only useful to attackers who are using information about underlying hardware fault (e.g. translation vs permission) as a mechanism to defeat KASLR. Remove the ESR context from the sigframe for user faults on kernel addresses. Cc: Ard Biesheuvel Cc: Dave Martin Signed-off-by: Will Deacon --- Here's another one that doesn't make a huge amount of difference when kpti is enabled, but I think is a change worth making all the same. arch/arm64/mm/fault.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 49dfb08a6c4d..b9800395788e 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -292,8 +292,10 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr, static void __do_user_fault(struct siginfo *info, unsigned int esr) { - current->thread.fault_address = (unsigned long)info->si_addr; - current->thread.fault_code = esr; + unsigned long addr = (unsigned long)info->si_addr; + + current->thread.fault_address = addr; + current->thread.fault_code = addr < TASK_SIZE ? esr : 0; arm64_force_sig_info(info, esr_to_fault_info(esr)->name, current); } -- 2.1.4