From nobody Sun Jun 14 09:58:36 2026 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F23EB3112C1 for ; Tue, 28 Apr 2026 21:01:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777410064; cv=none; b=Pn8w4ivWTPXUwFR6xecen/mi8ZzhmhPOH4b1xwC3BgowKOW/Xx/XsFp7/4v6f72zXlKizllCq3OfaeJ2BDTWe/4OYM/WLrMtobKk4O16QA7oL5zS0Ohx1PXdqSOcFK5N7jWlwwbC1yk/Q/6xbl+oLp0xa3CWcn9JVCjDzfdoOtk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777410064; c=relaxed/simple; bh=6GmWAmp4Qu6cDDdHDKUhXGhrc24fh9xWL2lFPSR72Nc=; h=Message-ID:Subject:From:To:Cc:Date:Content-Type:MIME-Version; b=U0MRv/LSFKxtlKzWqrsDJ86LmI4gG4JPYsQlenASsEWX9GMwFy6BGsMDPnNOkIRDt4ap1K0WESBdzQz4uXvNXEuP8qT0K+gLC7a6ehsH6/ZMk1rb2hPYWHgRBiUU5UXr2C23l87g+mnb5tzIx6b62mx0KomtlGPpCf9sZDJz4GY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=eKc/p7AT; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="eKc/p7AT" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:Date:Cc:To: From:Subject:Message-ID:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=YPQl5BVXffamppcPqN4s196/1UPL/Y4VqRKKr30eMl0=; b=eKc/p7ATblj5l7kQ3KL+Qu5X5x TMOMGyceslCo7kvm7+CVc2Jj3fR9qPZzeTBxvofXZAFC3WfVMGMF3xZEbEmyGyzFmivP76s9cvUQB tStwAoRbG4UEB2gj3LXn1MSg+ua4T62ZJF+NuzBjVDQMnFYihJNCnnGIZqGbvf+B92vWadYRolrhs S1c7GPxXzA2zFPVs+oQP4FWIYhnS7EDUwB91piob+5SZ1D6Dvwg/qX1TRiyHBsu3n/EMNcMk4NBxN D5TMDucwbpxI3VGTEvURLaSSuwO6WIV9pp0AGvKE4pc7YV8Cy/IoPr7dts9yHYBo+rytJJ0G62iqc /KAaePsg==; Received: from [172.31.31.148] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHpX7-000000045yN-1RVm; Tue, 28 Apr 2026 21:00:03 +0000 Message-ID: <32d627134143ffd957891cb697138e839c623211.camel@infradead.org> Subject: [PATCH v2] x86/kexec: Push kjump return address even for non-kjump kexec From: David Woodhouse To: Dave Hansen , Rohan Kakulawaram , kexec Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , David Woodhouse , Kai Huang , Paolo Bonzini , Uros Bizjak , Sohil Mehta , linux-kernel Date: Tue, 28 Apr 2026 21:59:52 +0100 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-gxU9ucmlKYxzjeBoeZFx" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-gxU9ucmlKYxzjeBoeZFx Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: David Woodhouse The version of purgatory code shipped by kexec-tools attempts to look above the top of its stack to find a return address for a kjump, even in a non-kjump kexec. Since commit 2cacf7f23a02 ("x86/kexec: Fix stack and handling of re-entry point for ::preserve_context") the word above the stack might not be there, leading to a fault (which is at least now caught by my exception-handling code in kexec). That commit fixed things for the actual kjump path, but no longer "gratuitously" pushes the unused return address to the stack in the non-kjump path. Put that *back* in the non-kjump path, to prevent purgatory from crashing when trying to access it. Reported-by: Rohan Kakulawaram Tested-by: Rohan Kakulawaram Fixes: 2cacf7f23a02 ("x86/kexec: Fix stack and handling of re-entry point f= or ::preserve_context") Signed-off-by: David Woodhouse Acked-by: Dave Hansen --- v2: Improve comment arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocat= e_kernel_64.S index 4ffba68dc57b..eaeb77464c06 100644 --- a/arch/x86/kernel/relocate_kernel_64.S +++ b/arch/x86/kernel/relocate_kernel_64.S @@ -136,6 +136,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) * %r13 original CR4 when relocate_kernel() was invoked */ =20 + /* + * Set return address to 0 if not preserving context. The purgatory + * shipped in kexec-tools will unconditionally look for the return + * address on the stack and set a kexec_jump_back_entry=3D command + * line option if it's non-zero. There's no other way that it can + * tell a preserve-context (kjump) kexec from a normal one. + */ + pushq $0 /* store the start address on the stack */ pushq %rdx =20 --=20 2.43.0 --=-gxU9ucmlKYxzjeBoeZFx Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 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