[Crash-utility] Re: [PATCH] Fix "irq -a" exceeding the memory range issue

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Hi Lianbo,

On Tue, Jul 16, 2024 at 11:19 AM Tao Liu <ltao@xxxxxxxxxx> wrote:
>
> Hi Lianbo,
>
> On Fri, Jul 12, 2024 at 6:32 PM Lianbo Jiang <lijiang@xxxxxxxxxx> wrote:
> >
> > Hi, Tao
> >
> > On 7/5/24 9:26 AM, devel-request@xxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
> > > Date: Thu,  4 Jul 2024 17:00:56 +1200
> > > From: Tao Liu<ltao@xxxxxxxxxx>
> > > Subject:  [PATCH] Fix "irq -a" exceeding the memory
> > >       range issue
> > > To:devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > Cc: Tao Liu<ltao@xxxxxxxxxx>
> > > Message-ID:<20240704050056.17375-1-ltao@xxxxxxxxxx>
> > > Content-Type: text/plain; charset="US-ASCII"; x-default=true
> > >
> > > Previously without the patch, there was an error observed as follows:
> > >
> > > crash> irq -a
> > > IRQ NAME                 AFFINITY
> > >    0 timer                0-191
> > >    4 ttyS0                0-23,96-119
> > > ...
> > >   84 smartpqi             72-73,168
> > > irq: page excluded: kernel virtual address: ffff97d03ffff000  type: "irq_desc affinity"
> > >
> > > The reason is the reading of irq affinity exceeded the memory range, see
> > > the following debug info:
> > >
> > > Thread 1 "crash" hit Breakpoint 1, generic_get_irq_affinity (irq=85) at kernel.c:7373
> > > 7375          irq_desc_addr = get_irq_desc_addr(irq);
> > > (gdb) p/x irq_desc_addr
> > > $1 = 0xffff97d03f21e800
> > >
> > > crash> struct irq_desc 0xffff97d03f21e800
> > > struct irq_desc {
> > >    irq_common_data = {
> > >      state_use_accessors = 425755136,
> > >      node = 3,
> > >      handler_data = 0x0,
> > >      msi_desc = 0xffff97ca51b83480,
> > >      affinity = 0xffff97d03fffee60,
> > >      effective_affinity = 0xffff97d03fffe6c0
> > >    },
> > >
> > > crash> whatis cpumask_t
> > > typedef struct cpumask {
> > >      unsigned long bits[128];
> > > } cpumask_t;
> > > SIZE: 1024
> > >
> > > In order to get the affinity, crash will read the memory range 0xffff97d03fffee60
> > > ~ 0xffff97d03fffee60 + 1024(0x400) by line:
> > >
> > >       readmem(affinity_ptr, KVADDR, affinity, len,
> > >               "irq_desc affinity", FAULT_ON_ERROR);
> > >
> > > However the reading will exceed the effective memory range:
> > >
> > > crash> kmem 0xffff97d03fffee60
> > > CACHE             OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE  NAME
> > > ffff97c900044400       32     123297    162944   1273     4k  kmalloc-32
> > >    SLAB              MEMORY            NODE  TOTAL  ALLOCATED  FREE
> > >    fffffca460ffff80  ffff97d03fffe000     3    128         81    47
> > >    FREE / [ALLOCATED]
> > >    [ffff97d03fffee60]
> > >
> > >        PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
> > > fffffca460ffff80 83fffe000 dead000000000001 ffff97d03fffe340  1 d7ffffe0000800 slab
> > >
> > > crash> kmem ffff97d03ffff000
> > >        PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
> > > fffffca460ffffc0 83ffff000                0        0  1 d7ffffe0004000 reserved
> > >
> > > crash> dmesg
> > > ...
> > > [    0.000000] BIOS-e820: [mem 0x00000000fe000000-0x00000000fe00ffff] reserved
> > > [    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000083fffefff] usable
> > > [    0.000000] BIOS-e820: [mem 0x000000083ffff000-0x000000083fffffff] reserved
> > > ...
> > >
> > > The beginning physical address, aka 0x83fffe000, is located in the usable
> > > area and is readable, however the later physical address, starting from
> > > 0x83ffff000, is located in reserved region and not readable. In fact,
> > > the affinity member is allocated by alloc_cpumask_var_node(), for the 192 CPUs
> > > system, the allocated size is only 24, and we can see it is within
> > > the kmalloc-32 slab. So it is incorrect to read 1024 length(given by
> > > STRUCT_SIZE("cpumask_t")), only 24 is enough.
> > >
> > > Since there are plenty of places in crash which takes the value of
> > > STRUCT_SIZE("cpumask_t"), and works fine for the past, this patch will
> > > not modify them all, but only this place which encountered the issue.
> > >
> > > Signed-off-by: Tao Liu<ltao@xxxxxxxxxx>
> > > ---
> > >   kernel.c | 9 ++++++---
> > >   1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/kernel.c b/kernel.c
> > > index 8a9d498..464e877 100644
> > > --- a/kernel.c
> > > +++ b/kernel.c
> > > @@ -7362,7 +7362,7 @@ void
> > >   generic_get_irq_affinity(int irq)
> > >   {
> > >       ulong irq_desc_addr;
> > > -     long len;
> > > +     long len, len_cpumask;
> > >       ulong affinity_ptr;
> > >       ulong *affinity;
> > >       ulong tmp_addr;
> > > @@ -7382,8 +7382,11 @@ generic_get_irq_affinity(int irq)
> > >       if (!action)
> > >               return;
> > >
> > > -     if ((len = STRUCT_SIZE("cpumask_t")) < 0)
> > > -             len = DIV_ROUND_UP(kt->cpus, BITS_PER_LONG) * sizeof(ulong);
> > > +     len = DIV_ROUND_UP(kt->cpus, BITS_PER_LONG) * sizeof(ulong);
> > > +     len_cpumask = STRUCT_SIZE("cpumask_t");
> > > +     if (len_cpumask > 0) {
> > > +             len = len_cpumask > len ? len : len_cpumask;
> > > +     }
> > >
> >
> > This change looks good, but I still have two comments below:
> >
> > [1] Can we drop the evaluation of "STRUCT_SIZE("cpumask_t")" and just
> > use the size of "DIV_ROUND_UP(kt->cpus, BITS_PER_LONG) * sizeof(ulong)"
> > ? Are there any regression issues?

I made a regression test, if all STRUCT_SIZE("cpumask_t") are replaced
by DIV_ROUND_UP(...), there are regression issues found, but I didn't
dive into the root cause of the failing reason.

>
> I'm not sure about the change, I will run a regression against it.
> >
> > [2] There are the similar case in the get_cpumask_buf(), see tools.c,
> > can you make the same change?

Yes, unlike [1], with only the similar case modified, no regressions
found. I will post v2 to include it.

Thanks,
Tao Liu

>
> Yes, I will give it a try to see if regressions are found.
>
> Thanks,
> Tao Liu
> >
> > ulong *
> > get_cpumask_buf(void)
> > {
> >          int cpulen;
> >          if ((cpulen = STRUCT_SIZE("cpumask_t")) < 0)
> >                  cpulen = DIV_ROUND_UP(kt->cpus, BITS_PER_LONG) *
> > sizeof(ulong);
> >          return (ulong *)GETBUF(cpulen);
> > }
> >
> > Any thoughts?
> >
> >
> > Thanks
> >
> > Lianbo
> >
> >
> > >       affinity = (ulong *)GETBUF(len);
> > >       if (VALID_MEMBER(irq_common_data_affinity))
> > > -- 2.40.1
> >
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