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From: Greg KH on 22 Apr 2010 16:10
2.6.33-stable review patch. If anyone has any objections, please let us know.

------------------

From: Alexey Starikovskiy <astarikovskiy(a)suse.de>

commit 2060c44576c79086ff24718878d7edaa7384a985 upstream.

access_bit_width field is u8 in ACPICA, thus 256 value written to it
becomes 0, causing divide by zero later.

Proper fix would be to remove access_bit_width at all, just because
we already have access_byte_width, which is access_bit_width / 8.
Limit access width to 64 bit for now.

https://bugzilla.kernel.org/show_bug.cgi?id=15749
fixes regression caused by the fix for:
https://bugzilla.kernel.org/show_bug.cgi?id=14667

Signed-off-by: Alexey Starikovskiy <astarikovskiy(a)suse.de>
Signed-off-by: Len Brown <len.brown(a)intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
drivers/acpi/acpica/exprep.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

--- a/drivers/acpi/acpica/exprep.c
+++ b/drivers/acpi/acpica/exprep.c
@@ -471,13 +471,18 @@ acpi_status acpi_ex_prep_field_value(str
/* allow full data read from EC address space */
if (obj_desc->field.region_obj->region.space_id ==
ACPI_ADR_SPACE_EC) {
- if (obj_desc->common_field.bit_length > 8)
- obj_desc->common_field.access_bit_width =
- ACPI_ROUND_UP(obj_desc->common_field.
- bit_length, 8);
+ if (obj_desc->common_field.bit_length > 8) {
+ unsigned width =
+ ACPI_ROUND_BITS_UP_TO_BYTES(
+ obj_desc->common_field.bit_length);
+ // access_bit_width is u8, don't overflow it
+ if (width > 8)
+ width = 8;
obj_desc->common_field.access_byte_width =
- ACPI_DIV_8(obj_desc->common_field.
- access_bit_width);
+ width;
+ obj_desc->common_field.access_bit_width =
+ 8 * width;
+ }
}

ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,


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