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Re: [XEN PATCH] tools/misc: xen-hvmcrash: Inject #DF instead of overwriting RIP
- To: Matthew Barnes <matthew.barnes@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 25 Jun 2024 22:02:42 +0100
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- Cc: Anthony PERARD <anthony@xxxxxxxxxxxxxx>
- Delivery-date: Tue, 25 Jun 2024 21:03:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03/06/2024 3:59 pm, Matthew Barnes wrote:
> xen-hvmcrash would previously save records, overwrite the instruction
> pointer with a bogus value, and then restore them to crash a domain
> just enough to cause the guest OS to memdump.
>
> This approach is found to be unreliable when tested on a guest running
> Windows 10 x64, with some executions doing nothing at all.
>
> Another approach would be to trigger NMIs. This approach is found to be
> unreliable when tested on Linux (Ubuntu 22.04), as Linux will ignore
> NMIs if it is not configured to handle such.
>
> Injecting a double fault abort to all vCPUs is found to be more
> reliable at crashing and invoking memdumps from Windows and Linux
> domains.
Why every CPU?
We never did that before, and I don't see any it ought to be necessary
now either.
> diff --git a/tools/misc/xen-hvmcrash.c b/tools/misc/xen-hvmcrash.c
> index 1d058fa40a47..8ef1beb388f8 100644
> --- a/tools/misc/xen-hvmcrash.c
> +++ b/tools/misc/xen-hvmcrash.c
> @@ -38,22 +38,21 @@
> #include <sys/stat.h>
> #include <arpa/inet.h>
>
> +#define XC_WANT_COMPAT_DEVICEMODEL_API
Please don't introduce this. We want to purge it from the codebase, not
propagate it.
You want to open and use a libxendevicemodel handle. (Sadly you also
need a xenctrl handle too, until we sort out the userspace ABIs).
> #include <xenctrl.h>
> #include <xen/xen.h>
> #include <xen/domctl.h>
> #include <xen/hvm/save.h>
>
> +#define X86_ABORT_DF 8
#include <xen/asm/x86-defns.h>
and use X86_EXC_DF.
~Andrew
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