Commit 39bc88e5 authored by Catalin Marinas's avatar Catalin Marinas
Browse files

arm64: Disable TTBR0_EL1 during normal kernel execution



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: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 4b65a5db
#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);
......
......@@ -23,6 +23,7 @@
#include <linux/sched.h>
#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
#include <asm/proc-fns.h>
#include <asm-generic/mm_hooks.h>
#include <asm/cputype.h>
......@@ -103,7 +104,7 @@ static inline void cpu_uninstall_idmap(void)
local_flush_tlb_all();
cpu_set_default_tcr_t0sz();
if (mm != &init_mm)
if (mm != &init_mm && !system_uses_ttbr0_pan())
cpu_switch_mm(mm->pgd, mm);
}
......@@ -163,20 +164,26 @@ enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
}
/*
* This is the actual mm switch as far as the scheduler
* is concerned. No registers are touched. We avoid
* calling the CPU specific function when the mm hasn't
* actually changed.
*/
static inline void
switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk)
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
static inline void update_saved_ttbr0(struct task_struct *tsk,
struct mm_struct *mm)
{
unsigned int cpu = smp_processor_id();
if (system_uses_ttbr0_pan()) {
BUG_ON(mm->pgd == swapper_pg_dir);
task_thread_info(tsk)->ttbr0 =
virt_to_phys(mm->pgd) | ASID(mm) << 48;
}
}
#else
static inline void update_saved_ttbr0(struct task_struct *tsk,
struct mm_struct *mm)
{
}
#endif
if (prev == next)
return;
static inline void __switch_mm(struct mm_struct *next)
{
unsigned int cpu = smp_processor_id();
/*
* init_mm.pgd does not contain any user mappings and it is always
......@@ -190,8 +197,26 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
check_and_switch_context(next, cpu);
}
static inline void
switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk)
{
if (prev != next)
__switch_mm(next);
/*
* Update the saved TTBR0_EL1 of the scheduled-in task as the previous
* value may have not been initialised yet (activate_mm caller) or the
* ASID has changed since the last run (following the context switch
* of another thread of the same process). Avoid setting the reserved
* TTBR0_EL1 to swapper_pg_dir (init_mm; e.g. via idle_task_exit).
*/
if (next != &init_mm)
update_saved_ttbr0(tsk, next);
}
#define deactivate_mm(tsk,mm) do { } while (0)
#define activate_mm(prev,next) switch_mm(prev, next, NULL)
#define activate_mm(prev,next) switch_mm(prev, next, current)
void verify_cpu_asid_bits(void);
......
......@@ -29,7 +29,9 @@
#include <asm/esr.h>
#include <asm/irq.h>
#include <asm/memory.h>
#include <asm/ptrace.h>
#include <asm/thread_info.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
/*
......@@ -108,6 +110,32 @@
mrs x22, elr_el1
mrs x23, spsr_el1
stp lr, x21, [sp, #S_LR]
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
/*
* Set the TTBR0 PAN bit in SPSR. When the exception is taken from
* EL0, there is no need to check the state of TTBR0_EL1 since
* accesses are always enabled.
* Note that the meaning of this bit differs from the ARMv8.1 PAN
* feature as all TTBR0_EL1 accesses are disabled, not just those to
* user mappings.
*/
alternative_if ARM64_HAS_PAN
b 1f // skip TTBR0 PAN
alternative_else_nop_endif
.if \el != 0
mrs x21, ttbr0_el1
tst x21, #0xffff << 48 // 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
and x23, x23, #~PSR_PAN_BIT // Clear the emulated PAN in the saved SPSR
.endif
__uaccess_ttbr0_disable x21
1:
#endif
stp x22, x23, [sp, #S_PC]
/*
......@@ -146,6 +174,40 @@
ldp x21, x22, [sp, #S_PC] // load ELR, SPSR
.if \el == 0
ct_user_enter
.endif
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
/*
* Restore access to TTBR0_EL1. If returning to EL0, no need for SPSR
* PAN bit checking.
*/
alternative_if ARM64_HAS_PAN
b 2f // skip TTBR0 PAN
alternative_else_nop_endif
.if \el != 0
tbnz x22, #22, 1f // Skip re-enabling TTBR0 access if the PSR_PAN_BIT is set
.endif
__uaccess_ttbr0_enable x0
.if \el == 0
/*
* Enable errata workarounds only if returning to user. The only
* workaround currently required for TTBR0_EL1 changes are for the
* Cavium erratum 27456 (broadcast TLBI instructions may cause I-cache
* corruption).
*/
post_ttbr0_update_workaround
.endif
1:
.if \el != 0
and x22, x22, #~PSR_PAN_BIT // ARMv8.0 CPUs do not understand this bit
.endif
2:
#endif
.if \el == 0
ldr x23, [sp, #S_SP] // load return stack pointer
msr sp_el0, x23
#ifdef CONFIG_ARM64_ERRATUM_845719
......@@ -161,6 +223,7 @@ alternative_if ARM64_WORKAROUND_845719
alternative_else_nop_endif
#endif
.endif
msr elr_el1, x21 // set up the return data
msr spsr_el1, x22
ldp x0, x1, [sp, #16 * 0]
......
......@@ -291,6 +291,15 @@ void __init setup_arch(char **cmdline_p)
smp_init_cpus();
smp_build_mpidr_hash();
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
/*
* Make sure init_thread_info.ttbr0 always generates translation
* faults in case uaccess_enable() is inadvertently called by the init
* thread.
*/
init_task.thread_info.ttbr0 = virt_to_phys(empty_zero_page);
#endif
#ifdef CONFIG_VT
#if defined(CONFIG_VGA_CONSOLE)
conswitchp = &vga_con;
......
......@@ -440,9 +440,10 @@ int cpu_enable_cache_maint_trap(void *__unused)
}
#define __user_cache_maint(insn, address, res) \
if (untagged_addr(address) >= user_addr_max()) \
if (untagged_addr(address) >= user_addr_max()) { \
res = -EFAULT; \
else \
} else { \
uaccess_ttbr0_enable(); \
asm volatile ( \
"1: " insn ", %1\n" \
" mov %w0, #0\n" \
......@@ -454,7 +455,9 @@ int cpu_enable_cache_maint_trap(void *__unused)
" .popsection\n" \
_ASM_EXTABLE(1b, 3b) \
: "=r" (res) \
: "r" (address), "i" (-EFAULT) )
: "r" (address), "i" (-EFAULT)); \
uaccess_ttbr0_disable(); \
}
static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
{
......
......@@ -23,6 +23,7 @@
#include <asm/assembler.h>
#include <asm/cpufeature.h>
#include <asm/alternative.h>
#include <asm/uaccess.h>
/*
* flush_icache_range(start,end)
......@@ -48,6 +49,7 @@ ENTRY(flush_icache_range)
* - end - virtual end address of region
*/
ENTRY(__flush_cache_user_range)
uaccess_ttbr0_enable x2, x3
dcache_line_size x2, x3
sub x3, x2, #1
bic x4, x0, x3
......@@ -69,10 +71,12 @@ USER(9f, ic ivau, x4 ) // invalidate I line PoU
dsb ish
isb
mov x0, #0
1:
uaccess_ttbr0_disable x1
ret
9:
mov x0, #-EFAULT
ret
b 1b
ENDPROC(flush_icache_range)
ENDPROC(__flush_cache_user_range)
......
......@@ -221,7 +221,12 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu)
raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
switch_mm_fastpath:
cpu_switch_mm(mm->pgd, mm);
/*
* Defer TTBR0_EL1 setting for user threads to uaccess_enable() when
* emulating PAN.
*/
if (!system_uses_ttbr0_pan())
cpu_switch_mm(mm->pgd, mm);
}
static int asids_init(void)
......
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