From e7a062e77db3af4973188853de2f1c27ee08bf7a Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 10 Jan 2018 13:18:30 +0000 Subject: arm64: kpti: Fix the interaction between ASID switching and software PAN Commit 6b88a32c7af6 upstream. With ARM64_SW_TTBR0_PAN enabled, the exception entry code checks the active ASID to decide whether user access was enabled (non-zero ASID) when the exception was taken. On return from exception, if user access was previously disabled, it re-instates TTBR0_EL1 from the per-thread saved value (updated in switch_mm() or efi_set_pgd()). Commit 7655abb95386 ("arm64: mm: Move ASID from TTBR0 to TTBR1") makes a TTBR0_EL1 + ASID switching non-atomic. Subsequently, commit 27a921e75711 ("arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN") changes the __uaccess_ttbr0_disable() function and asm macro to first write the reserved TTBR0_EL1 followed by the ASID=0 update in TTBR1_EL1. If an exception occurs between these two, the exception return code will re-instate a valid TTBR0_EL1. Similar scenario can happen in cpu_switch_mm() between setting the reserved TTBR0_EL1 and the ASID update in cpu_do_switch_mm(). This patch reverts the entry.S check for ASID == 0 to TTBR0_EL1 and disables the interrupts around the TTBR0_EL1 and ASID switching code in __uaccess_ttbr0_disable(). It also ensures that, when returning from the EFI runtime services, efi_set_pgd() doesn't leave a non-zero ASID in TTBR1_EL1 by using uaccess_ttbr0_{enable,disable}. The accesses to current_thread_info()->ttbr0 are updated to use READ_ONCE/WRITE_ONCE. As a safety measure, __uaccess_ttbr0_enable() always masks out any existing non-zero ASID TTBR1_EL1 before writing in the new ASID. Fixes: 27a921e75711 ("arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN") Acked-by: Will Deacon Reported-by: Ard Biesheuvel Tested-by: Ard Biesheuvel Reviewed-by: James Morse Tested-by: James Morse Co-developed-by: Marc Zyngier Signed-off-by: Catalin Marinas Signed-off-by: Will Deacon Conflicts: arch/arm64/include/asm/asm-uaccess.h arch/arm64/include/asm/uaccess.h Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/entry.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/arm64/kernel') diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 6ceed4877daf..06476e8da1ca 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -204,7 +204,7 @@ alternative_if ARM64_HAS_PAN alternative_else_nop_endif .if \el != 0 - mrs x21, ttbr1_el1 + mrs x21, ttbr0_el1 tst x21, #TTBR_ASID_MASK // Check for the reserved ASID orr x23, x23, #PSR_PAN_BIT // Set the emulated PAN in the saved SPSR b.eq 1f // TTBR0 access already disabled -- cgit v1.2.3