xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

arm64: Disable TTBR0_EL1 during normal kernel execution

Browse Source 
When the TTBR0 PAN feature is enabled, the kernel entry points need to
disable access to TTBR0_EL1. The PAN status of the interrupted context
is stored as part of the saved pstate, reusing the PSR_PAN_BIT (22).
Restoring access to TTBR0_EL1 is done on exception return if returning
to user or returning to a context where PAN was disabled.

Context switching via switch_mm() must defer the update of TTBR0_EL1
until a return to user or an explicit uaccess_enable() call.

Special care needs to be taken for two cases where TTBR0_EL1 is set
outside the normal kernel context switch operation: EFI run-time
services (via efi_set_pgd) and CPU suspend (via cpu_(un)install_idmap).
Code has been added to avoid deferred TTBR0_EL1 switching as in
switch_mm() and restore the reserved TTBR0_EL1 when uninstalling the
special TTBR0_EL1.

User cache maintenance (user_cache_maint_handler and
__flush_cache_user_range) needs the TTBR0_EL1 re-instated since the
operations are performed by user virtual address.

This patch also removes a stale comment on the switch_mm() function.

Cc: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Catalin Marinas
2016-09-02 14:54:03 +01:00
parent 4b65a5db36
commit 39bc88e5e3
7 changed files with 153 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
arch/arm64/include/asm/efi.h
View File

@@ -1,6 +1,7 @@
#ifndef _ASM_EFI_H
#define _ASM_EFI_H
#include <asm/cpufeature.h>
#include <asm/io.h>
#include <asm/mmu_context.h>
#include <asm/neon.h>
@@ -75,7 +76,30 @@ static inline void efifb_setup_from_dmi(struct screen_info *si, const char *opt)
static inline void efi_set_pgd(struct mm_struct *mm)
{
switch_mm(NULL, mm, NULL);
__switch_mm(mm);
if (system_uses_ttbr0_pan()) {
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.
*/
update_saved_ttbr0(current, mm);
cpu_switch_mm(mm->pgd, mm);
} 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
* (if different from init_mm).
*/
cpu_set_reserved_ttbr0();
if (current->active_mm != &init_mm)
update_saved_ttbr0(current, current->active_mm);
}
}
}
void efi_virtmap_load(void);