lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Mon, 7 Mar 2016 16:02:15 -0800 From: Greg KH <gregkh@...uxfoundation.org> To: Gabriel Somlo <somlo@....edu> Cc: "Michael S. Tsirkin" <mst@...hat.com>, robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com, ijc+devicetree@...lion.org.uk, galak@...eaurora.org, arnd@...db.de, lersek@...hat.com, ralf@...ux-mips.org, rmk+kernel@....linux.org.uk, eric@...olt.net, hanjun.guo@...aro.org, zajec5@...il.com, sudeep.holla@....com, agross@...eaurora.org, linux-api@...r.kernel.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, qemu-devel@...gnu.org, imammedo@...hat.com, peter.maydell@...aro.org, leif.lindholm@...aro.org, ard.biesheuvel@...aro.org, pbonzini@...hat.com, kraxel@...hat.com, ehabkost@...hat.com, luto@...capital.net, stefanha@...il.com, revol@...e.fr, matt@...eblueprint.co.uk, rth@...ddle.net Subject: Re: [RFC PATCH] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access On Mon, Mar 07, 2016 at 06:55:43PM -0500, Gabriel Somlo wrote: > Allowing for the future possibility of implementing AML-based > (i.e., firmware-triggered) access to the QEMU fw_cfg device, > acquire the global ACPI lock when accessing the device on behalf > of the guest-side sysfs driver, to prevent any potential race > conditions. > > Suggested-by: Michael S. Tsirkin <mst@...hat.com> > Signed-off-by: Gabriel Somlo <somlo@....edu> > --- > > Turns out, there *is* a way to acquire a global ACPI lock from within > a "random" kernel driver after all. Luckily I have a healthy dose of > respect for Michael's opinions :) so I kept circling back through > existing kernel sources for an example I can use, and I think this > might be it. > > I'm posting as RFC because I'm not really confident about assessing > the likelihood of there ever being a race condition between the kernel > fw_cfg sysfs driver and firmware on my own. Obviously Michael has > concerns about it, but any additional opinions from the QEMU camp would > be much appreciated. > > Thanks again, > --Gabriel > > drivers/firmware/qemu_fw_cfg.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c > index 7bba76c..cc4c27a 100644 > --- a/drivers/firmware/qemu_fw_cfg.c > +++ b/drivers/firmware/qemu_fw_cfg.c > @@ -77,12 +77,26 @@ static inline u16 fw_cfg_sel_endianness(u16 key) > static inline void fw_cfg_read_blob(u16 key, > void *buf, loff_t pos, size_t count) > { > +#ifdef CONFIG_ACPI > + u32 glk; > + int status; > + status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk); Why not fix up the ACPI api to not require #ifdef here? It should be added to a .h file somewhere instead. > + if (ACPI_FAILURE(status)) { > + /* Should never get here */ > + WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n"); > + memset(buf, 0, count); > + return; > + } > +#endif > mutex_lock(&fw_cfg_dev_lock); > iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl); > while (pos-- > 0) > ioread8(fw_cfg_reg_data); > ioread8_rep(fw_cfg_reg_data, buf, count); > mutex_unlock(&fw_cfg_dev_lock); > +#ifdef CONFIG_ACPI > + acpi_release_global_lock(glk); Same here. thanks, greg k-h
Powered by blists - more mailing lists