[Qemu-devel] [PATCH] hw/s390x/ipl: Fix crash that occurs when -kernel is used with small images

[Qemu-devel] [PATCH] hw/s390x/ipl: Fix crash that occurs when -kernel is used with small images

[Thomas Huth]

Add a sanity check to fix the following crash:

$ echo "Insane in the mainframe" > /tmp/test.txt
$ s390x-softmmu/qemu-system-s390x -nographic -kernel /tmp/test.txt
Segmentation fault (core dumped)

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 hw/s390x/ipl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
index 04245b5..9bb9b50 100644
--- a/hw/s390x/ipl.c
+++ b/hw/s390x/ipl.c
@@ -168,7 +168,8 @@ static void s390_ipl_realize(DeviceState *dev, Error **errp)
          * we can not rely on the ELF entry point - it was 0x800 (the SALIPL
          * loader) and it won't work. For this case we force it to 0x10000, too.
          */
-        if (pentry == KERN_IMAGE_START || pentry == 0x800) {
+        if ((pentry == KERN_IMAGE_START || pentry == 0x800) &&
+            kernel_size > KERN_PARM_AREA + strlen(ipl->cmdline)) {
             ipl->start_addr = KERN_IMAGE_START;
             /* Overwrite parameters in the kernel image, which are "rom" */
             strcpy(rom_ptr(KERN_PARM_AREA), ipl->cmdline);
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] hw/s390x/ipl: Fix crash that occurs when -kernel is used with small images

[Christian Borntraeger]

On 06/10/2018 03:12 PM, Thomas Huth wrote:
> Add a sanity check to fix the following crash:
> 
> $ echo "Insane in the mainframe" > /tmp/test.txt
> $ s390x-softmmu/qemu-system-s390x -nographic -kernel /tmp/test.txt
> Segmentation fault (core dumped)
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>

I think a similar problem exists for INITRD_PARM_START and INITRD_PARM_SIZE. No?


> ---
>  hw/s390x/ipl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
> index 04245b5..9bb9b50 100644
> --- a/hw/s390x/ipl.c
> +++ b/hw/s390x/ipl.c
> @@ -168,7 +168,8 @@ static void s390_ipl_realize(DeviceState *dev, Error **errp)
>           * we can not rely on the ELF entry point - it was 0x800 (the SALIPL
>           * loader) and it won't work. For this case we force it to 0x10000, too.
>           */
> -        if (pentry == KERN_IMAGE_START || pentry == 0x800) {
> +        if ((pentry == KERN_IMAGE_START || pentry == 0x800) &&
> +            kernel_size > KERN_PARM_AREA + strlen(ipl->cmdline)) {
>              ipl->start_addr = KERN_IMAGE_START;
>              /* Overwrite parameters in the kernel image, which are "rom" */
>              strcpy(rom_ptr(KERN_PARM_AREA), ipl->cmdline);
> 

Re: [Qemu-devel] [PATCH] hw/s390x/ipl: Fix crash that occurs when -kernel is used with small images

[Cornelia Huck]

On Mon, 11 Jun 2018 09:49:39 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 06/10/2018 03:12 PM, Thomas Huth wrote:
> > Add a sanity check to fix the following crash:
> > 
> > $ echo "Insane in the mainframe" > /tmp/test.txt
> > $ s390x-softmmu/qemu-system-s390x -nographic -kernel /tmp/test.txt
> > Segmentation fault (core dumped)
> > 
> > Signed-off-by: Thomas Huth <thuth@redhat.com>  
> 
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> 
> I think a similar problem exists for INITRD_PARM_START and INITRD_PARM_SIZE. No?

I think so as well.

> 
> 
> > ---
> >  hw/s390x/ipl.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
> > index 04245b5..9bb9b50 100644
> > --- a/hw/s390x/ipl.c
> > +++ b/hw/s390x/ipl.c
> > @@ -168,7 +168,8 @@ static void s390_ipl_realize(DeviceState *dev, Error **errp)
> >           * we can not rely on the ELF entry point - it was 0x800 (the SALIPL
> >           * loader) and it won't work. For this case we force it to 0x10000, too.
> >           */
> > -        if (pentry == KERN_IMAGE_START || pentry == 0x800) {
> > +        if ((pentry == KERN_IMAGE_START || pentry == 0x800) &&
> > +            kernel_size > KERN_PARM_AREA + strlen(ipl->cmdline)) {
> >              ipl->start_addr = KERN_IMAGE_START;
> >              /* Overwrite parameters in the kernel image, which are "rom" */
> >              strcpy(rom_ptr(KERN_PARM_AREA), ipl->cmdline);
> >   
> 

The outcome of this is that we don't write into areas we must not write
into, but we still have a broken "kernel" and will simply fail if the
thing we're pointing to isn't a valid PSW. I guess that's what we want
("crap in, crap out"), i.e. no fallback to the bios or something like
that?

Re: [Qemu-devel] [PATCH] hw/s390x/ipl: Fix crash that occurs when -kernel is used with small images

[Thomas Huth]

On 11.06.2018 11:24, Cornelia Huck wrote:
> On Mon, 11 Jun 2018 09:49:39 +0200
> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
>> On 06/10/2018 03:12 PM, Thomas Huth wrote:
>>> Add a sanity check to fix the following crash:
>>>
>>> $ echo "Insane in the mainframe" > /tmp/test.txt
>>> $ s390x-softmmu/qemu-system-s390x -nographic -kernel /tmp/test.txt
>>> Segmentation fault (core dumped)
>>>
>>> Signed-off-by: Thomas Huth <thuth@redhat.com>  
>>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>
>> I think a similar problem exists for INITRD_PARM_START and INITRD_PARM_SIZE. No?
> 
> I think so as well.

You're right:

$ s390x-softmmu/qemu-system-s390x -kernel /tmp/test.txt \
                                  -initrd /tmp/test.txt
Segmentation fault (core dumped)

Shall I sent a v2 of this patch, or do you prefer a separate patch for
that issue?

>>> ---
>>>  hw/s390x/ipl.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
>>> index 04245b5..9bb9b50 100644
>>> --- a/hw/s390x/ipl.c
>>> +++ b/hw/s390x/ipl.c
>>> @@ -168,7 +168,8 @@ static void s390_ipl_realize(DeviceState *dev, Error **errp)
>>>           * we can not rely on the ELF entry point - it was 0x800 (the SALIPL
>>>           * loader) and it won't work. For this case we force it to 0x10000, too.
>>>           */
>>> -        if (pentry == KERN_IMAGE_START || pentry == 0x800) {
>>> +        if ((pentry == KERN_IMAGE_START || pentry == 0x800) &&
>>> +            kernel_size > KERN_PARM_AREA + strlen(ipl->cmdline)) {
>>>              ipl->start_addr = KERN_IMAGE_START;
>>>              /* Overwrite parameters in the kernel image, which are "rom" */
>>>              strcpy(rom_ptr(KERN_PARM_AREA), ipl->cmdline);
> 
> The outcome of this is that we don't write into areas we must not write
> into, but we still have a broken "kernel" and will simply fail if the
> thing we're pointing to isn't a valid PSW. I guess that's what we want
> ("crap in, crap out"), i.e. no fallback to the bios or something like
> that?

Yes, I think "crap in, crap out" is ok here. Theoretically, the user
could also have a self-made micro-kernel that is just one byte smaller
than KERN_PARM_AREA, and this would still work with this patch, so no
need for an extra error message in that case.

 Thomas

Re: [Qemu-devel] [PATCH] hw/s390x/ipl: Fix crash that occurs when -kernel is used with small images

[Christian Borntraeger]

On 06/11/2018 12:08 PM, Thomas Huth wrote:
> On 11.06.2018 11:24, Cornelia Huck wrote:
>> On Mon, 11 Jun 2018 09:49:39 +0200
>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>>
>>> On 06/10/2018 03:12 PM, Thomas Huth wrote:
>>>> Add a sanity check to fix the following crash:
>>>>
>>>> $ echo "Insane in the mainframe" > /tmp/test.txt
>>>> $ s390x-softmmu/qemu-system-s390x -nographic -kernel /tmp/test.txt
>>>> Segmentation fault (core dumped)
>>>>
>>>> Signed-off-by: Thomas Huth <thuth@redhat.com>  
>>>
>>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>
>>> I think a similar problem exists for INITRD_PARM_START and INITRD_PARM_SIZE. No?
>>
>> I think so as well.
> 
> You're right:
> 
> $ s390x-softmmu/qemu-system-s390x -kernel /tmp/test.txt \
>                                   -initrd /tmp/test.txt
> Segmentation fault (core dumped)
> 
> Shall I sent a v2 of this patch, or do you prefer a separate patch for
> that issue?

Whatever is easier for you.

> 
>>>> ---
>>>>  hw/s390x/ipl.c | 3 ++-
>>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
>>>> index 04245b5..9bb9b50 100644
>>>> --- a/hw/s390x/ipl.c
>>>> +++ b/hw/s390x/ipl.c
>>>> @@ -168,7 +168,8 @@ static void s390_ipl_realize(DeviceState *dev, Error **errp)
>>>>           * we can not rely on the ELF entry point - it was 0x800 (the SALIPL
>>>>           * loader) and it won't work. For this case we force it to 0x10000, too.
>>>>           */
>>>> -        if (pentry == KERN_IMAGE_START || pentry == 0x800) {
>>>> +        if ((pentry == KERN_IMAGE_START || pentry == 0x800) &&
>>>> +            kernel_size > KERN_PARM_AREA + strlen(ipl->cmdline)) {
>>>>              ipl->start_addr = KERN_IMAGE_START;
>>>>              /* Overwrite parameters in the kernel image, which are "rom" */
>>>>              strcpy(rom_ptr(KERN_PARM_AREA), ipl->cmdline);
>>
>> The outcome of this is that we don't write into areas we must not write
>> into, but we still have a broken "kernel" and will simply fail if the
>> thing we're pointing to isn't a valid PSW. I guess that's what we want
>> ("crap in, crap out"), i.e. no fallback to the bios or something like
>> that?
> 
> Yes, I think "crap in, crap out" is ok here. Theoretically, the user
> could also have a self-made micro-kernel that is just one byte smaller
> than KERN_PARM_AREA, and this would still work with this patch, so no
> need for an extra error message in that case.