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Subject[patch 02/10] x86/mce: Disable tracing and kprobes on do_machine_check()
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);

#ifndef CONFIG_MEMORY_FAILURE
int memory_failure(unsigned long pfn, int flags)
@@ -1892,10 +1899,11 @@ static void unexpected_machine_check(str
void (*machine_check_vector)(struct pt_regs *, long error_code) =
unexpected_machine_check;

-dotraplinkage void do_mce(struct pt_regs *regs, long error_code)
+dotraplinkage notrace void do_mce(struct pt_regs *regs, long error_code)
{
machine_check_vector(regs, error_code);
}
+NOKPROBE_SYMBOL(do_mce);

/*
* Called for each booted CPU to set up machine checks.
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