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From:   "Bae, Chang Seok" <chang.seok.bae@intel.com>
To:     Borislav Petkov <bp@alien8.de>
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Subject: Re: [PATCH v8 5/6] x86/signal: Detect and prevent an alternate signal
 stack overflow
Thread-Topic: [PATCH v8 5/6] x86/signal: Detect and prevent an alternate
 signal stack overflow
Thread-Index: AQHXNzOQXxUM6Mub30elxTKCBjQG3areurqAgAGVlAA=
Date:   Wed, 12 May 2021 18:48:11 +0000
Message-ID: <B8EF2379-0AF6-4D00-B6B8-214CA9073BFC@intel.com>
References: <20210422044856.27250-1-chang.seok.bae@intel.com>
 <20210422044856.27250-6-chang.seok.bae@intel.com> <YJrOsbyYhMndI5jd@zn.tnic>
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On May 11, 2021, at 11:36, Borislav Petkov <bp@alien8.de> wrote:
>=20
> I clumsily tried to register a SIGSEGV handler with
>=20
>        act.sa_sigaction =3D my_sigsegv;
>        sigaction(SIGSEGV, &act, NULL);
>=20
> but that doesn't fire - task gets killed. Maybe I'm doing it wrong.

Since the altstack is already overflowed, perhaps set the flag like this --=
 not
using it to get the handler:

	act.sa_sigaction =3D my_sigsegv;
+	act.sa_flags =3D SA_SIGINFO;
	sigaction(SIGSEGV, &act, NULL);

FWIW, I think this is just a workaround for this case; in practice, altstac=
k is
rather a backup for normal stack corruption.

Thanks,
Chang