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authorCatalin Marinas <catalin.marinas@arm.com>2018-01-10 13:18:30 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2018-01-16 17:37:48 +0000
commit6b88a32c7af68895134872cdec3b6bfdb532d94e (patch)
tree506f26d64992edfcf1344ab22d3b68794e607d3d /arch/arm64/mm
parent558daf693e0c7ea118dbfb9539aa5a72f34bad2e (diff)
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 <will.deacon@arm.com> Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: James Morse <james.morse@arm.com> Tested-by: James Morse <james.morse@arm.com> Co-developed-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64/mm')
-rw-r--r--arch/arm64/mm/cache.S2
-rw-r--r--arch/arm64/mm/proc.S3
2 files changed, 4 insertions, 1 deletions
diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index 6cd20a8c0952..91464e7f77cc 100644
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -72,7 +72,7 @@ USER(9f, ic ivau, x4 ) // invalidate I line PoU
isb
mov x0, #0
1:
- uaccess_ttbr0_disable x1
+ uaccess_ttbr0_disable x1, x2
ret
9:
mov x0, #-EFAULT
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 05e4ae934b23..c6a12073ef46 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -153,6 +153,9 @@ ENDPROC(cpu_do_resume)
ENTRY(cpu_do_switch_mm)
mrs x2, ttbr1_el1
mmid x1, x1 // get mm->context.id
+#ifdef CONFIG_ARM64_SW_TTBR0_PAN
+ bfi x0, x1, #48, #16 // set the ASID field in TTBR0
+#endif
bfi x2, x1, #48, #16 // set the ASID
msr ttbr1_el1, x2 // in TTBR1 (since TCR.A1 is set)
isb