linux-kernel - Re: [PATCH 1/1] fbdev: hyperv_fb: iounmap() the correct memory when removing a device

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250210145825.GA12377@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Mon, 10 Feb 2025 06:58:25 -0800
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.com>
Cc: "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>,
	"decui@...rosoft.com" <decui@...rosoft.com>,
	"deller@....de" <deller@....de>,
	"weh@...rosoft.com" <weh@...rosoft.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: Re: [PATCH 1/1] fbdev: hyperv_fb: iounmap() the correct memory when
 removing a device

On Mon, Feb 10, 2025 at 02:28:35PM +0000, Michael Kelley wrote:
> From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com> Sent: Monday, February 10, 2025 4:41 AM
> > 
> > On Sun, Feb 09, 2025 at 03:52:52PM -0800, mhkelley58@...il.com wrote:
> > > From: Michael Kelley <mhklinux@...look.com>
> > >
> > > When a Hyper-V framebuffer device is removed, or the driver is unbound
> > > from a device, any allocated and/or mapped memory must be released. In
> > > particular, MMIO address space that was mapped to the framebuffer must
> > > be unmapped. Current code unmaps the wrong address, resulting in an
> > > error like:
> > >
> > > [ 4093.980597] iounmap: bad address 00000000c936c05c
> > >
> > > followed by a stack dump.
> > >
> > > Commit d21987d709e8 ("video: hyperv: hyperv_fb: Support deferred IO for
> > > Hyper-V frame buffer driver") changed the kind of address stored in
> > > info->screen_base, and the iounmap() call in hvfb_putmem() was not
> > > updated accordingly.
> > >
> > > Fix this by updating hvfb_putmem() to unmap the correct address.
> > >
> > > Fixes: d21987d709e8 ("video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver")
> > > Signed-off-by: Michael Kelley <mhklinux@...look.com>
> > > ---
> > >  drivers/video/fbdev/hyperv_fb.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> > > index 7fdb5edd7e2e..363e4ccfcdb7 100644
> > > --- a/drivers/video/fbdev/hyperv_fb.c
> > > +++ b/drivers/video/fbdev/hyperv_fb.c
> > > @@ -1080,7 +1080,7 @@ static void hvfb_putmem(struct hv_device *hdev, struct fb_info *info)
> > >
> > >  	if (par->need_docopy) {
> > >  		vfree(par->dio_vp);
> > > -		iounmap(info->screen_base);
> > > +		iounmap(par->mmio_vp);
> > >  		vmbus_free_mmio(par->mem->start, screen_fb_size);
> > >  	} else {
> > >  		hvfb_release_phymem(hdev, info->fix.smem_start,
> > > --
> > > 2.25.1
> > >
> > 
> > Thanks for fixing this:
> > Reviewed-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> > 
> > 
> > While we are at it, I want to mention that I also observed below WARN
> > while removing the hyperv_fb, but that needs a separate fix.
> > 
> > 
> > [   44.111220] WARNING: CPU: 35 PID: 1882 at drivers/video/fbdev/core/fb_info.c:70 framebuffer_release+0x2c/0x40
> > < snip >
> > [   44.111289] Call Trace:
> > [   44.111290]  <TASK>
> > [   44.111291]  ? show_regs+0x6c/0x80
> > [   44.111295]  ? __warn+0x8d/0x150
> > [   44.111298]  ? framebuffer_release+0x2c/0x40
> > [   44.111300]  ? report_bug+0x182/0x1b0
> > [   44.111303]  ? handle_bug+0x6e/0xb0
> > [   44.111306]  ? exc_invalid_op+0x18/0x80
> > [   44.111308]  ? asm_exc_invalid_op+0x1b/0x20
> > [   44.111311]  ? framebuffer_release+0x2c/0x40
> > [   44.111313]  ? hvfb_remove+0x86/0xa0 [hyperv_fb]
> > [   44.111315]  vmbus_remove+0x24/0x40 [hv_vmbus]
> > [   44.111323]  device_remove+0x40/0x80
> > [   44.111325]  device_release_driver_internal+0x20b/0x270
> > [   44.111327]  ? bus_find_device+0xb3/0xf0
> > 
> 
> Thanks for pointing this out. Interestingly, I'm not seeing this WARN
> in my experiments. What base kernel are you testing with? Are you
> testing on a local VM or in Azure? What exactly are you doing
> to create the problem? I've been doing unbind of the driver,
> but maybe you are doing something different.
> 
> FWIW, there is yet another issue where after doing two unbind/bind
> cycles of the hyperv_fb driver, there's an error about freeing a
> non-existent resource. I know what that problem is, and it's in
> vmbus_drv.c. I'll be submitting a patch for that as soon as I figure out
> a clean fix.
> 
> Michael

This is on local Hyper-V. Kernel: 6.14.0-rc1-next-20250205+
I run below command to reproduce the above error:
echo "5620e0c7-8062-4dce-aeb7-520c7ef76171" > /sys/bus/vmbus/devices/5620e0c7-8062-4dce-aeb7-520c7ef76171/driver/unbind

When hvfb_remove is called I can see the refcount for framebuffer is 2 when ,
I expect it to be 1. After unregistering this framebuffer there is still 1 refcount
remains, which is the reason for this WARN at the time of framebuffer_release.

I wonder who is registering/using this extra framebuffer. Its not hyperv_drm or
hyperv_fb IIUC.

- Saurabh