[PATCH 3/3] x86/mm, tracing: Fix CR2 corruption
From: root
Date: Wed Jul 03 2019 - 06:29:07 EST
Despire 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.
Ideally we'll clean up the entry code by moving this tracing and
context tracking nonsense into C some day, but let's not delay fixing
this longer.
Reported-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
Reported-by: Eiichi Tsukata <devel@xxxxxxxxxxxx>
Debugged-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/x86/entry/entry_32.S | 25 ++++++++++++++++++++++---
arch/x86/entry/entry_64.S | 28 ++++++++++++++--------------
arch/x86/include/asm/kvm_para.h | 2 +-
arch/x86/include/asm/traps.h | 2 +-
arch/x86/kernel/kvm.c | 8 ++++----
arch/x86/mm/fault.c | 28 ++++++++++------------------
6 files changed, 52 insertions(+), 41 deletions(-)
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1443,9 +1443,28 @@ BUILD_INTERRUPT3(hv_stimer0_callback_vec
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:
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -901,7 +901,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work
* @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
@@ -937,18 +937,27 @@ ENTRY(\sym)
.if \paranoid
call paranoid_entry
+ /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */
.else
call error_entry
.endif
UNWIND_HINT_REGS
- /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */
- .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 */
@@ -1180,10 +1189,10 @@ idtentry xenint3 do_int3 has_error_co
#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
@@ -1338,18 +1347,9 @@ 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
/*
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -92,7 +92,7 @@ void kvm_async_pf_task_wait(u32 token, i
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);
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -81,7 +81,7 @@ struct bad_iret_stack *fixup_bad_iret(st
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);
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -242,23 +242,23 @@ EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_
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;
}
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1513,7 +1513,7 @@ NOKPROBE_SYMBOL(do_user_addr_fault);
* and the problem, and then passes it off to one of the appropriate
* routines.
*/
-static noinline void
+static __always_inline void
__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
unsigned long address)
{
@@ -1528,35 +1528,27 @@ __do_page_fault(struct pt_regs *regs, un
else
do_user_addr_fault(regs, hw_error_code, address);
}
-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);
}