Messages in this thread | | | Subject | Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine_check() | From | Andy Lutomirski <> | Date | Tue, 25 Feb 2020 21:29:00 -0800 |
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On 2/25/20 5:13 PM, Frederic Weisbecker wrote: > On Tue, Feb 25, 2020 at 10:36:38PM +0100, Thomas Gleixner wrote: >> From: Andy Lutomirski <luto@kernel.org> >> >> do_machine_check() can be raised in almost any context including the most >> fragile ones. Prevent kprobes and tracing. >> >> Signed-off-by: Andy Lutomirski <luto@kernel.org> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> >> --- >> arch/x86/include/asm/traps.h | 3 --- >> arch/x86/kernel/cpu/mce/core.c | 12 ++++++++++-- >> 2 files changed, 10 insertions(+), 5 deletions(-) >> >> --- a/arch/x86/include/asm/traps.h >> +++ b/arch/x86/include/asm/traps.h >> @@ -88,9 +88,6 @@ dotraplinkage void do_page_fault(struct >> 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); >> -#ifdef CONFIG_X86_MCE >> -dotraplinkage void do_machine_check(struct pt_regs *regs, long error_code); >> -#endif >> dotraplinkage void do_simd_coprocessor_error(struct pt_regs *regs, long error_code); >> #ifdef CONFIG_X86_32 >> dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code); >> --- a/arch/x86/kernel/cpu/mce/core.c >> +++ b/arch/x86/kernel/cpu/mce/core.c >> @@ -1213,8 +1213,14 @@ static void __mc_scan_banks(struct mce * >> * On Intel systems this is entered on all CPUs in parallel through >> * MCE broadcast. However some CPUs might be broken beyond repair, >> * so be always careful when synchronizing with others. >> + * >> + * Tracing and kprobes are disabled: if we interrupted a kernel context >> + * with IF=1, we need to minimize stack usage. There are also recursion >> + * issues: if the machine check was due to a failure of the memory >> + * backing the user stack, tracing that reads the user stack will cause >> + * potentially infinite recursion. >> */ >> -void do_machine_check(struct pt_regs *regs, long error_code) >> +void notrace do_machine_check(struct pt_regs *regs, long error_code) >> { >> DECLARE_BITMAP(valid_banks, MAX_NR_BANKS); >> DECLARE_BITMAP(toclear, MAX_NR_BANKS); >> @@ -1360,6 +1366,7 @@ void do_machine_check(struct pt_regs *re >> ist_exit(regs); >> } >> EXPORT_SYMBOL_GPL(do_machine_check); >> +NOKPROBE_SYMBOL(do_machine_check); > > That won't protect all the function called by do_machine_check(), right? > There are lots of them. >
It at least means we can survive to run actual C code in do_machine_check(), which lets us try to mitigate this issue further. PeterZ has patches for that, and maybe this series fixes it later on. (I'm reading in order!)
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