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acpi/x86: ignore unspecified bit positions in the ACPI global lock field

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commit ecb9c790999fd6c5af0f44783bd0217f0b89ec2b upstream.

The value in "new" is constructed from "old" such that all bits defined
as reserved by the ACPI spec[1] are left untouched. But if those bits
do not happen to be all zero, "new < 3" will not evaluate to true.

The firmware of the laptop(s) Medion MD63490 / Akoya P15648 comes with
garbage inside the "FACS" ACPI table. The starting value is
old=0x4944454d, therefore new=0x4944454e, which is >= 3. Mask off
the reserved bits.

[1] https://uefi.org/sites/default/files/resources/ACPI_6_2.pdf

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206553
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jan Engelhardt 2020-03-05 13:24:25 +01:00 committed by Greg Kroah-Hartman
parent f562b19f32
commit 6d70133202
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/acpi/boot.c
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@ -1717,7 +1717,7 @@ int __acpi_acquire_global_lock(unsigned int *lock)
new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1));
val = cmpxchg(lock, old, new);
} while (unlikely (val != old));
return (new < 3) ? -1 : 0;
return ((new & 0x3) < 3) ? -1 : 0;
}
int __acpi_release_global_lock(unsigned int *lock)