Commit a6e2c226 authored May 24, 2020 by Aneesh Kumar K.V Committed by Michael Ellerman Jun 15, 2020

powerpc: Fix kernel crash in show_instructions() w/DEBUG_VIRTUAL



With CONFIG_DEBUG_VIRTUAL=y, we can hit a BUG() if we take a hard
lockup watchdog interrupt when in OPAL mode.

This happens in show_instructions() if the kernel takes the watchdog
NMI IPI, or any other interrupt, with MSR_IR == 0. show_instructions()
updates the variable pc in the loop and the second iteration will
result in BUG().

We hit the BUG_ON due the below check in  __va()

  #define __va(x)
  ({
  	VIRTUAL_BUG_ON((unsigned long)(x) >= PAGE_OFFSET);
  	(void *)(unsigned long)((phys_addr_t)(x) | PAGE_OFFSET);
  })

Fix it by moving the check out of the loop. Also update nip so that
the nip == pc check still matches.

Fixes: 4dd7554a ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
[mpe: Use IS_ENABLED(), massage change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200524093822.423487-1-aneesh.kumar@linux.ibm.com

parent b3a9e3b9

arch/powerpc/kernel/process.c

+11 −9

Original line number	Diff line number	Diff line
		@@ -1252,29 +1252,31 @@ struct task_struct __switch_to(struct task_struct prev,
		static void show_instructions(struct pt_regs *regs)
		{
		int i;
		unsigned long nip = regs->nip;
		unsigned long pc = regs->nip - (NR_INSN_TO_PRINT * 3 / 4 * sizeof(int));

		printk("Instruction dump:");

		/*
		* If we were executing with the MMU off for instructions, adjust pc
		* rather than printing XXXXXXXX.
		*/
		if (!IS_ENABLED(CONFIG_BOOKE) && !(regs->msr & MSR_IR)) {
		pc = (unsigned long)phys_to_virt(pc);
		nip = (unsigned long)phys_to_virt(regs->nip);
		}

		for (i = 0; i < NR_INSN_TO_PRINT; i++) {
		int instr;

		if (!(i % 8))
		pr_cont("\n");

		#if !defined(CONFIG_BOOKE)
		/* If executing with the IMMU off, adjust pc rather
		* than print XXXXXXXX.
		*/
		if (!(regs->msr & MSR_IR))
		pc = (unsigned long)phys_to_virt(pc);
		#endif

		if (!__kernel_text_address(pc) \|\|
		probe_kernel_address((const void *)pc, instr)) {
		pr_cont("XXXXXXXX ");
		} else {
		if (regs->nip == pc)
		if (nip == pc)
		pr_cont("<%08x> ", instr);
		else
		pr_cont("%08x ", instr);

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