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Date: Fri, 28 Oct 2016 18:27:14 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Will Deacon <will.deacon@....com>,
James Morse <james.morse@....com>,
Kees Cook <keescook@...omium.org>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
AKASHI Takahiro <takahiro.akashi@...aro.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v4 6/8] arm64: Handle faults caused by inadvertent user access with PAN enabled
When TTBR0_EL1 is set to the reserved page, an erroneous kernel access
to user space would generate a translation fault. This patch adds the
checks for the software-set PSR_PAN_BIT to emulate a permission fault
and report it accordingly.
Cc: Will Deacon <will.deacon@....com>
Cc: James Morse <james.morse@....com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Mark Rutland <mark.rutland@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
arch/arm64/mm/fault.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index d035cc594445..a78a5c401806 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -269,13 +269,19 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
return fault;
}
-static inline bool is_permission_fault(unsigned int esr)
+static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs)
{
unsigned int ec = ESR_ELx_EC(esr);
unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE;
- return (ec == ESR_ELx_EC_DABT_CUR && fsc_type == ESR_ELx_FSC_PERM) ||
- (ec == ESR_ELx_EC_IABT_CUR && fsc_type == ESR_ELx_FSC_PERM);
+ if (ec != ESR_ELx_EC_DABT_CUR && ec != ESR_ELx_EC_IABT_CUR)
+ return false;
+
+ if (system_uses_ttbr0_pan())
+ return fsc_type == ESR_ELx_FSC_FAULT &&
+ (regs->pstate & PSR_PAN_BIT);
+ else
+ return fsc_type == ESR_ELx_FSC_PERM;
}
static bool is_el0_instruction_abort(unsigned int esr)
@@ -315,7 +321,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
mm_flags |= FAULT_FLAG_WRITE;
}
- if (is_permission_fault(esr) && (addr < USER_DS)) {
+ if (addr < USER_DS && is_permission_fault(esr, regs)) {
/* regs->orig_addr_limit may be 0 if we entered from EL0 */
if (regs->orig_addr_limit == KERNEL_DS)
die("Accessing user space memory with fs=KERNEL_DS", regs, esr);
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