[Crash-utility] [PATCH] x86_64: Fix check for __per_cpu_offset initialisation

[lijiang]

>
> Date: Thu,  5 Aug 2021 15:19:37 +0200
> From: Philipp Rudo <prudo at redhat.com>
> To: crash-utility at redhat.com
> Subject: [Crash-utility] [PATCH] x86_64: Fix check for
>         __per_cpu_offset        initialisation
> Message-ID: <20210805131937.5051-1-prudo at redhat.com>
>
> Since at least kernel v2.6.30 the __per_cpu_offset gets initialized to
> __per_cpu_load. So first check if the __per_cpu_offset was set to a
> proper value before reading any per cpu variable to prevent potential
> bugs.
>
>
Hi, Philipp

Thank you for the patch. Can you help to describe  more details about the
potential risks? and what conditions might trigger the potential bugs?

Did you mean that it's related to the crash live analysis issue(1978032)? I
tried to reproduce it, but so far I haven't reproduced it with the upstream
kernel.

Thanks.
Lianbo


> Signed-off-by: Philipp Rudo <prudo at redhat.com>
> ---
>  x86_64.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/x86_64.c b/x86_64.c
> index 6eb7d67..0bb8705 100644
> --- a/x86_64.c
> +++ b/x86_64.c
> @@ -1327,6 +1327,8 @@ x86_64_per_cpu_init(void)
>                 ms->stkinfo.isize = 16384;
>
>         for (i = cpus = 0; i < NR_CPUS; i++) {
> +               if (kt->__per_cpu_offset[i] ==
> symbol_value("__per_cpu_load"))
> +                       break;
>                 if (!readmem(cpu_sp->value + kt->__per_cpu_offset[i],
>                     KVADDR, &cpunumber, sizeof(int),
>                     "cpu number (per_cpu)", QUIET|RETURN_ON_ERROR))
> @@ -5602,7 +5604,7 @@ x86_64_get_smp_cpus(void)
>                         return 1;
>
>                 for (i = cpus = 0; i < NR_CPUS; i++) {
> -                       if (kt->__per_cpu_offset[i] == 0)
> +                       if (kt->__per_cpu_offset[i] ==
> symbol_value("__per_cpu_load"))
>                                 break;
>                         if (!readmem(sp->value + kt->__per_cpu_offset[i],
>                             KVADDR, &cpunumber, sizeof(int),
> --
> 2.31.1
>
>
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