On Fri, Jan 15, 2016 at 5:27 AM, Jean Delvare <jdelvare@xxxxxxx> wrote: > Hi Andy, > > Sorry for the late reply. > > On Wed, 13 Jan 2016 14:28:18 -0800, Andy Lutomirski wrote: >> [cc: Jean Delvare] >> >> On Tue, Jan 12, 2016 at 6:25 AM, Pali Rohár <pali.rohar@xxxxxxxxx> wrote: >> > On Monday 11 January 2016 13:58:20 Andy Lutomirski wrote: >> >> On Sun, Jan 3, 2016 at 6:52 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: >> >> > The dmi_walk function maps the DMI table, walks it, and unmaps it. >> >> > This means that the dell_bios_hotkey_table that find_hk_type stores >> >> > points to unmapped memory by the time it gets read. >> >> > >> >> > I've been able to trigger crashes caused by the stale pointer a >> >> > couple of times, but never on a stock kernel. >> >> > >> >> > Fix it by generating the keymap in the dmi_walk callback instead of >> >> > storing a pointer. >> >> >> >> Quick ping: has anyone had a chance to look at this? >> > >> > Hi Andy, I looked at this patch, but I think some people from -mm or DMI >> > code should look at it as it is memory problem... We also has one in >> > dell-laptop.ko (wrong API usage) and so -mm people could know it better. >> >> Let's ask: >> >> Jean, am I right that drivers must not store pointers to DMI tables >> that they find through dmi_walk? > > Yes, you are right. > >> Is there any alternative interface >> that could be used to get a longer-lived pointer to DMI tables, or >> should drivers just parse them and copy out any info needed from the >> dmi_walk callback? > > There is no alternative for OEM type records. Drivers are indeed > expected to copy the information they need to their own buffers. FWIW, especially if we consider mapping it persistently, maybe we should use ioremap_prot and map it both cached and ro. Actually, switching to a cached mapping regardless of persistence could noticeably help boot times. UC accesses are very, very slow. --Andy -- To unsubscribe from this list: send the line "unsubscribe platform-driver-x86" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
