x86/nmi: Enable nested do_nmi() handling for 64-bit kernels
32-bit kernels handle nested NMIs in C. Enable the exact same handling on 64-bit kernels as well. This isn't currently necessary, but it will become necessary once the asm code starts allowing limited nesting. Signed-off-by: Andy Lutomirski <luto@kernel.org> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Borislav Petkov <bp@suse.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski
Ingo Molnar
parent
21bdb584af
commit
9d05041679
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@ -408,15 +408,15 @@ static void default_do_nmi(struct pt_regs *regs)
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NOKPROBE_SYMBOL(default_do_nmi);
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/*
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* NMIs can hit breakpoints which will cause it to lose its
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* NMI context with the CPU when the breakpoint does an iret.
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*/
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#ifdef CONFIG_X86_32
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/*
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* For i386, NMIs use the same stack as the kernel, and we can
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* add a workaround to the iret problem in C (preventing nested
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* NMIs if an NMI takes a trap). Simply have 3 states the NMI
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* can be in:
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* NMIs can hit breakpoints which will cause it to lose its NMI context
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* with the CPU when the breakpoint or page fault does an IRET.
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*
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* As a result, NMIs can nest if NMIs get unmasked due an IRET during
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* NMI processing. On x86_64, the asm glue protects us from nested NMIs
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* if the outer NMI came from kernel mode, but we can still nest if the
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* outer NMI came from user mode.
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*
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* To handle these nested NMIs, we have three states:
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*
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* 1) not running
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* 2) executing
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@ -430,15 +430,14 @@ NOKPROBE_SYMBOL(default_do_nmi);
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* (Note, the latch is binary, thus multiple NMIs triggering,
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* when one is running, are ignored. Only one NMI is restarted.)
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*
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* If an NMI hits a breakpoint that executes an iret, another
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* NMI can preempt it. We do not want to allow this new NMI
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* to run, but we want to execute it when the first one finishes.
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* We set the state to "latched", and the exit of the first NMI will
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* perform a dec_return, if the result is zero (NOT_RUNNING), then
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* it will simply exit the NMI handler. If not, the dec_return
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* would have set the state to NMI_EXECUTING (what we want it to
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* be when we are running). In this case, we simply jump back
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* to rerun the NMI handler again, and restart the 'latched' NMI.
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* If an NMI executes an iret, another NMI can preempt it. We do not
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* want to allow this new NMI to run, but we want to execute it when the
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* first one finishes. We set the state to "latched", and the exit of
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* the first NMI will perform a dec_return, if the result is zero
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* (NOT_RUNNING), then it will simply exit the NMI handler. If not, the
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* dec_return would have set the state to NMI_EXECUTING (what we want it
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* to be when we are running). In this case, we simply jump back to
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* rerun the NMI handler again, and restart the 'latched' NMI.
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*
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* No trap (breakpoint or page fault) should be hit before nmi_restart,
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* thus there is no race between the first check of state for NOT_RUNNING
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@ -461,49 +460,36 @@ enum nmi_states {
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static DEFINE_PER_CPU(enum nmi_states, nmi_state);
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static DEFINE_PER_CPU(unsigned long, nmi_cr2);
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#define nmi_nesting_preprocess(regs) \
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do { \
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if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { \
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this_cpu_write(nmi_state, NMI_LATCHED); \
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return; \
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} \
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this_cpu_write(nmi_state, NMI_EXECUTING); \
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this_cpu_write(nmi_cr2, read_cr2()); \
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} while (0); \
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nmi_restart:
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#define nmi_nesting_postprocess() \
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do { \
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if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \
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write_cr2(this_cpu_read(nmi_cr2)); \
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if (this_cpu_dec_return(nmi_state)) \
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goto nmi_restart; \
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} while (0)
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#else /* x86_64 */
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#ifdef CONFIG_X86_64
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/*
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* In x86_64 things are a bit more difficult. This has the same problem
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* where an NMI hitting a breakpoint that calls iret will remove the
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* NMI context, allowing a nested NMI to enter. What makes this more
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* difficult is that both NMIs and breakpoints have their own stack.
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* When a new NMI or breakpoint is executed, the stack is set to a fixed
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* point. If an NMI is nested, it will have its stack set at that same
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* fixed address that the first NMI had, and will start corrupting the
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* stack. This is handled in entry_64.S, but the same problem exists with
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* the breakpoint stack.
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* In x86_64, we need to handle breakpoint -> NMI -> breakpoint. Without
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* some care, the inner breakpoint will clobber the outer breakpoint's
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* stack.
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*
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* If a breakpoint is being processed, and the debug stack is being used,
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* if an NMI comes in and also hits a breakpoint, the stack pointer
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* will be set to the same fixed address as the breakpoint that was
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* interrupted, causing that stack to be corrupted. To handle this case,
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* check if the stack that was interrupted is the debug stack, and if
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* so, change the IDT so that new breakpoints will use the current stack
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* and not switch to the fixed address. On return of the NMI, switch back
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* to the original IDT.
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* If a breakpoint is being processed, and the debug stack is being
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* used, if an NMI comes in and also hits a breakpoint, the stack
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* pointer will be set to the same fixed address as the breakpoint that
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* was interrupted, causing that stack to be corrupted. To handle this
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* case, check if the stack that was interrupted is the debug stack, and
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* if so, change the IDT so that new breakpoints will use the current
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* stack and not switch to the fixed address. On return of the NMI,
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* switch back to the original IDT.
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*/
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static DEFINE_PER_CPU(int, update_debug_stack);
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#endif
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static inline void nmi_nesting_preprocess(struct pt_regs *regs)
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dotraplinkage notrace void
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do_nmi(struct pt_regs *regs, long error_code)
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{
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if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
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this_cpu_write(nmi_state, NMI_LATCHED);
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return;
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}
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this_cpu_write(nmi_state, NMI_EXECUTING);
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this_cpu_write(nmi_cr2, read_cr2());
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nmi_restart:
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#ifdef CONFIG_X86_64
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/*
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* If we interrupted a breakpoint, it is possible that
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* the nmi handler will have breakpoints too. We need to
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@ -514,22 +500,8 @@ static inline void nmi_nesting_preprocess(struct pt_regs *regs)
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debug_stack_set_zero();
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this_cpu_write(update_debug_stack, 1);
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}
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}
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static inline void nmi_nesting_postprocess(void)
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{
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if (unlikely(this_cpu_read(update_debug_stack))) {
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debug_stack_reset();
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this_cpu_write(update_debug_stack, 0);
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}
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}
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#endif
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dotraplinkage notrace void
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do_nmi(struct pt_regs *regs, long error_code)
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{
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nmi_nesting_preprocess(regs);
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nmi_enter();
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inc_irq_stat(__nmi_count);
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@ -539,8 +511,17 @@ do_nmi(struct pt_regs *regs, long error_code)
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nmi_exit();
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/* On i386, may loop back to preprocess */
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nmi_nesting_postprocess();
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#ifdef CONFIG_X86_64
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if (unlikely(this_cpu_read(update_debug_stack))) {
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debug_stack_reset();
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this_cpu_write(update_debug_stack, 0);
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}
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#endif
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if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
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write_cr2(this_cpu_read(nmi_cr2));
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if (this_cpu_dec_return(nmi_state))
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goto nmi_restart;
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}
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NOKPROBE_SYMBOL(do_nmi);
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