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x86/debug: Prevent data breakpoints on __per_cpu_offset

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commit c4bed4b969 upstream.

When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU GSBASE value
via __per_cpu_offset or pcpu_unit_offsets.

When a data breakpoint is set on __per_cpu_offset[cpu] (read-write
operation), the specific CPU will be stuck in an infinite #DB loop.

RCU will try to send an NMI to the specific CPU, but it is not working
either since NMI also relies on paranoid_entry(). Which means it's
undebuggable.

Fixes: eaad981291ee3("x86/entry/64: Introduce the FIND_PERCPU_BASE macro")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210204152708.21308-1-jiangshanlai@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Lai Jiangshan 2021-02-04 23:27:06 +08:00 committed by Greg Kroah-Hartman
parent c000dcfb3a
commit b796770c6d
1 changed files with 14 additions and 0 deletions
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14
arch/x86/kernel/hw_breakpoint.c
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@ -269,6 +269,20 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
CPU_ENTRY_AREA_TOTAL_SIZE))
return true;
/*
* When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
* GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
*/
#ifdef CONFIG_SMP
if (within_area(addr, end, (unsigned long)__per_cpu_offset,
sizeof(unsigned long) * nr_cpu_ids))
return true;
#else
if (within_area(addr, end, (unsigned long)&pcpu_unit_offsets,
sizeof(pcpu_unit_offsets)))
return true;
#endif
for_each_possible_cpu(cpu) {
/* The original rw GDT is being used after load_direct_gdt() */
if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),