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libahci: Fix possible Spectre-v1 pmp indexing in ahci_led_store() 

Currently smatch warns of possible Spectre-V1 issue in ahci_led_store():
drivers/ata/libahci.c:1150 ahci_led_store() warn: potential spectre issue 'pp->em_priv' (local cap)

Userspace controls @pmp from following callchain:
em_message->store()
->ata_scsi_em_message_store()
-->ap->ops->em_store()
--->ahci_led_store()

After the mask+shift @pmp is effectively an 8b value, which is used to
index into an array of length 8, so sanitize the array index.

Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
John Garry 2018-06-08 18:26:33 +08:00 committed by Tejun Heo
parent 9ffc59d572
commit fae2a63737
1 changed files with 5 additions and 2 deletions
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7
drivers/ata/libahci.c
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@ -35,6 +35,7 @@
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/module.h>
#include <linux/nospec.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
@ -1146,10 +1147,12 @@ static ssize_t ahci_led_store(struct ata_port *ap, const char *buf,
/* get the slot number from the message */
pmp = (state & EM_MSG_LED_PMP_SLOT) >> 8;
if (pmp < EM_MAX_SLOTS)
if (pmp < EM_MAX_SLOTS) {
pmp = array_index_nospec(pmp, EM_MAX_SLOTS);
emp = &pp->em_priv[pmp];
else
} else {
return -EINVAL;
}
/* mask off the activity bits if we are in sw_activity
* mode, user should turn off sw_activity before setting