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dc4e0021b0
There are three problems with the current layout of the doublefault
stack and TSS. First, the TSS is only cacheline-aligned, which is
not enough -- if the hardware portion of the TSS (struct x86_hw_tss)
crosses a page boundary, horrible things happen [0]. Second, the
stack and TSS are global, so simultaneous double faults on different
CPUs will cause massive corruption. Third, the whole mechanism
won't work if user CR3 is loaded, resulting in a triple fault [1].
Let the doublefault stack and TSS share a page (which prevents the
TSS from spanning a page boundary), make it percpu, and move it into
cpu_entry_area. Teach the stack dump code about the doublefault
stack.
[0] Real hardware will read past the end of the page onto the next
*physical* page if a task switch happens. Virtual machines may
have any number of bugs, and I would consider it reasonable for
a VM to summarily kill the guest if it tries to task-switch to
a page-spanning TSS.
[1] Real hardware triple faults. At least some VMs seem to hang.
I'm not sure what's going on.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
14 lines
308 B
C
14 lines
308 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_DOUBLEFAULT_H
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#define _ASM_X86_DOUBLEFAULT_H
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#if defined(CONFIG_X86_32) && defined(CONFIG_DOUBLEFAULT)
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extern void doublefault_init_cpu_tss(void);
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#else
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static inline void doublefault_init_cpu_tss(void)
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{
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}
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#endif
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#endif /* _ASM_X86_DOUBLEFAULT_H */
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