From 6b88a32c7af68895134872cdec3b6bfdb532d94e 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 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 --- arch/arm64/include/asm/efi.h | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) (limited to 'arch/arm64/include/asm/efi.h') diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h index c4cd5081d78b..8389050328bb 100644 --- a/arch/arm64/include/asm/efi.h +++ b/arch/arm64/include/asm/efi.h @@ -121,19 +121,21 @@ static inline void efi_set_pgd(struct mm_struct *mm) if (mm != current->active_mm) { /* * Update the current thread's saved ttbr0 since it is - * restored as part of a return from exception. Set - * the hardware TTBR0_EL1 using cpu_switch_mm() - * directly to enable potential errata workarounds. + * restored as part of a return from exception. Enable + * access to the valid TTBR0_EL1 and invoke the errata + * workaround directly since there is no return from + * exception when invoking the EFI run-time services. */ update_saved_ttbr0(current, mm); - cpu_switch_mm(mm->pgd, mm); + uaccess_ttbr0_enable(); + post_ttbr_update_workaround(); } else { /* * Defer the switch to the current thread's TTBR0_EL1 * until uaccess_enable(). Restore the current * thread's saved ttbr0 corresponding to its active_mm */ - cpu_set_reserved_ttbr0(); + uaccess_ttbr0_disable(); update_saved_ttbr0(current, current->active_mm); } } -- cgit v1.2.3