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x86/mm, tracing: Fix CR2 corruption

Browse source 
Despite the current efforts to read CR2 before tracing happens there still
exist a number of possible holes:

  idtentry page_fault             do_page_fault           has_error_code=1
    call error_entry
      TRACE_IRQS_OFF
        call trace_hardirqs_off*
          #PF // modifies CR2

      CALL_enter_from_user_mode
        __context_tracking_exit()
          trace_user_exit(0)
            #PF // modifies CR2

    call do_page_fault
      address = read_cr2(); /* whoopsie */

And similar for i386.

Fix it by pulling the CR2 read into the entry code, before any of that
stuff gets a chance to run and ruin things.

Reported-by: He Zhe <zhe.he@windriver.com>
Reported-by: Eiichi Tsukata <devel@etsukata.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: bp@alien8.de
Cc: rostedt@goodmis.org
Cc: torvalds@linux-foundation.org
Cc: hpa@zytor.com
Cc: dave.hansen@linux.intel.com
Cc: jgross@suse.com
Cc: joel@joelfernandes.org
Link: https://lkml.kernel.org/r/20190711114336.116812491@infradead.org

Debugged-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Peter Zijlstra 2019-07-11 13:40:59 +02:00 committed by Thomas Gleixner
parent 4234653e88
commit a0d14b8909
7 changed files with 59 additions and 51 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

25
arch/x86/entry/entry_32.S
View file

@ -1443,9 +1443,28 @@ BUILD_INTERRUPT3(hv_stimer0_callback_vector, HYPERV_STIMER0_VECTOR,
ENTRY(page_fault)
ASM_CLAC
pushl $do_page_fault
ALIGN
jmp common_exception
pushl $0; /* %gs's slot on the stack */
SAVE_ALL switch_stacks=1 skip_gs=1
ENCODE_FRAME_POINTER
UNWIND_ESPFIX_STACK
/* fixup %gs */
GS_TO_REG %ecx
REG_TO_PTGS %ecx
SET_KERNEL_GS %ecx
GET_CR2_INTO(%ecx) # might clobber %eax
/* fixup orig %eax */
movl PT_ORIG_EAX(%esp), %edx # get the error code
movl $-1, PT_ORIG_EAX(%esp) # no syscall to restart
TRACE_IRQS_OFF
movl %esp, %eax # pt_regs pointer
call do_page_fault
jmp ret_from_exception
END(page_fault)
common_exception:

35
arch/x86/entry/entry_64.S
View file

@ -864,7 +864,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
*/
#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + (x) * 8)
.macro idtentry_part do_sym, has_error_code:req, paranoid:req, shift_ist=-1, ist_offset=0
.macro idtentry_part do_sym, has_error_code:req, read_cr2:req, paranoid:req, shift_ist=-1, ist_offset=0
.if \paranoid
call paranoid_entry
@ -874,12 +874,21 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
.endif
UNWIND_HINT_REGS
.if \paranoid
.if \read_cr2
GET_CR2_INTO(%rdx); /* can clobber %rax */
.endif
.if \shift_ist != -1
TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */
.else
TRACE_IRQS_OFF
.endif
.if \paranoid == 0
testb $3, CS(%rsp)
jz .Lfrom_kernel_no_context_tracking_\@
CALL_enter_from_user_mode
.Lfrom_kernel_no_context_tracking_\@:
.endif
movq %rsp, %rdi /* pt_regs pointer */
@ -923,6 +932,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
* fresh stack. (This is for #DB, which has a nasty habit
* of recursing.)
* @create_gap: create a 6-word stack gap when coming from kernel mode.
* @read_cr2: load CR2 into the 3rd argument; done before calling any C code
*
* idtentry generates an IDT stub that sets up a usable kernel context,
* creates struct pt_regs, and calls @do_sym. The stub has the following
@ -947,7 +957,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
* @paranoid == 2 is special: the stub will never switch stacks. This is for
* #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS.
*/
.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ist_offset=0 create_gap=0
.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ist_offset=0 create_gap=0 read_cr2=0
ENTRY(\sym)
UNWIND_HINT_IRET_REGS offset=\has_error_code*8
@ -985,7 +995,7 @@ ENTRY(\sym)
.Lfrom_usermode_no_gap_\@:
.endif
idtentry_part \do_sym, \has_error_code, \paranoid, \shift_ist, \ist_offset
idtentry_part \do_sym, \has_error_code, \read_cr2, \paranoid, \shift_ist, \ist_offset
.if \paranoid == 1
/*
@ -994,7 +1004,7 @@ ENTRY(\sym)
* run in real process context if user_mode(regs).
*/
.Lfrom_usermode_switch_stack_\@:
idtentry_part \do_sym, \has_error_code, paranoid=0
idtentry_part \do_sym, \has_error_code, \read_cr2, paranoid=0
.endif
_ASM_NOKPROBE(\sym)
@ -1006,7 +1016,7 @@ idtentry overflow do_overflow has_error_code=0
idtentry bounds do_bounds has_error_code=0
idtentry invalid_op do_invalid_op has_error_code=0
idtentry device_not_available do_device_not_available has_error_code=0
idtentry double_fault do_double_fault has_error_code=1 paranoid=2
idtentry double_fault do_double_fault has_error_code=1 paranoid=2 read_cr2=1
idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0
idtentry invalid_TSS do_invalid_TSS has_error_code=1
idtentry segment_not_present do_segment_not_present has_error_code=1
@ -1179,10 +1189,10 @@ idtentry xenint3 do_int3 has_error_code=0
#endif
idtentry general_protection do_general_protection has_error_code=1
idtentry page_fault do_page_fault has_error_code=1
idtentry page_fault do_page_fault has_error_code=1 read_cr2=1
#ifdef CONFIG_KVM_GUEST
idtentry async_page_fault do_async_page_fault has_error_code=1
idtentry async_page_fault do_async_page_fault has_error_code=1 read_cr2=1
#endif
#ifdef CONFIG_X86_MCE
@ -1281,18 +1291,9 @@ ENTRY(error_entry)
movq %rax, %rsp /* switch stack */
ENCODE_FRAME_POINTER
pushq %r12
/*
* We need to tell lockdep that IRQs are off. We can't do this until
* we fix gsbase, and we should do it before enter_from_user_mode
* (which can take locks).
*/
TRACE_IRQS_OFF
CALL_enter_from_user_mode
ret
.Lerror_entry_done:
TRACE_IRQS_OFF
ret
/*

2
arch/x86/include/asm/kvm_para.h
View file

@ -92,7 +92,7 @@ void kvm_async_pf_task_wait(u32 token, int interrupt_kernel);
void kvm_async_pf_task_wake(u32 token);
u32 kvm_read_and_reset_pf_reason(void);
extern void kvm_disable_steal_time(void);
void do_async_page_fault(struct pt_regs *regs, unsigned long error_code);
void do_async_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address);
#ifdef CONFIG_PARAVIRT_SPINLOCKS
void __init kvm_spinlock_init(void);

4
arch/x86/include/asm/traps.h
View file

@ -74,14 +74,14 @@ dotraplinkage void do_invalid_TSS(struct pt_regs *regs, long error_code);
dotraplinkage void do_segment_not_present(struct pt_regs *regs, long error_code);
dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code);
#ifdef CONFIG_X86_64
dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code);
dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long address);
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs);
asmlinkage __visible notrace
struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s);
void __init trap_init(void);
#endif
dotraplinkage void do_general_protection(struct pt_regs *regs, long error_code);
dotraplinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code);
dotraplinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address);
dotraplinkage void do_spurious_interrupt_bug(struct pt_regs *regs, long error_code);
dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code);
dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code);

8
arch/x86/kernel/kvm.c
View file

@ -242,23 +242,23 @@ EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason);
dotraplinkage void
do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
do_async_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
enum ctx_state prev_state;
switch (kvm_read_and_reset_pf_reason()) {
default:
do_page_fault(regs, error_code);
do_page_fault(regs, error_code, address);
break;
case KVM_PV_REASON_PAGE_NOT_PRESENT:
/* page is swapped out by the host. */
prev_state = exception_enter();
kvm_async_pf_task_wait((u32)read_cr2(), !user_mode(regs));
kvm_async_pf_task_wait((u32)address, !user_mode(regs));
exception_exit(prev_state);
break;
case KVM_PV_REASON_PAGE_READY:
rcu_irq_enter();
kvm_async_pf_task_wake((u32)read_cr2());
kvm_async_pf_task_wake((u32)address);
rcu_irq_exit();
break;
}

6
arch/x86/kernel/traps.c
View file

@ -313,13 +313,10 @@ __visible void __noreturn handle_stack_overflow(const char *message,
#ifdef CONFIG_X86_64
/* Runs on IST stack */
dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2)
{
static const char str[] = "double fault";
struct task_struct *tsk = current;
#ifdef CONFIG_VMAP_STACK
unsigned long cr2;
#endif
#ifdef CONFIG_X86_ESPFIX64
extern unsigned char native_irq_return_iret[];
@ -415,7 +412,6 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
* stack even if the actual trigger for the double fault was
* something else.
*/
cr2 = read_cr2();
if ((unsigned long)task_stack_page(tsk) - 1 - cr2 < PAGE_SIZE)
handle_stack_overflow("kernel stack overflow (double-fault)", regs, cr2);
#endif

30
arch/x86/mm/fault.c
View file

@ -1507,9 +1507,8 @@ void do_user_addr_fault(struct pt_regs *regs,
NOKPROBE_SYMBOL(do_user_addr_fault);
/*
* This routine handles page faults. It determines the address,
* and the problem, and then passes it off to one of the appropriate
* routines.
* Explicitly marked noinline such that the function tracer sees this as the
* page_fault entry point.
*/
static noinline void
__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
@ -1528,33 +1527,26 @@ __do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
}
NOKPROBE_SYMBOL(__do_page_fault);
static nokprobe_inline void
trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
unsigned long error_code)
static __always_inline void
trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
if (!trace_pagefault_enabled())
return;
if (user_mode(regs))
trace_page_fault_user(address, regs, error_code);
else
trace_page_fault_kernel(address, regs, error_code);
}
/*
* We must have this function blacklisted from kprobes, tagged with notrace
* and call read_cr2() before calling anything else. To avoid calling any
* kind of tracing machinery before we've observed the CR2 value.
*
* exception_{enter,exit}() contains all sorts of tracepoints.
*/
dotraplinkage void notrace
do_page_fault(struct pt_regs *regs, unsigned long error_code)
dotraplinkage void
do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
unsigned long address = read_cr2(); /* Get the faulting address */
enum ctx_state prev_state;
prev_state = exception_enter();
if (trace_pagefault_enabled())
trace_page_fault_entries(address, regs, error_code);
trace_page_fault_entries(regs, error_code, address);
__do_page_fault(regs, error_code, address);
exception_exit(prev_state);
}