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x-conformance=sidf_compatible IronPort-SDR: n/ntTUMBHdXfDhIsaZ//MzxxQ+rF4cFJL1QaSTcBG5CvludCFNnttdzeRxDBOD2vuL0SRotDCL x5f55ExKUEpm64w6sodE/IoN81GVpOuJxFjyXjAg8PA9TiG2BWdPR4ChTDpJ/MazAo9zYQD+K3 AGDtczbxFxKJIu+ehxssdbX7zVzpY1TbXLsU0KnTnhpb10VLV4rY0jfEbj2jh5Mh6tYGOEuQwC 3HqydbyZalgBrW1kY7sw1bABPQyaUAjIrXIJHbqqgqdLqchUW6u8xt0hZQX/9JQJNbXRNkrcUk JhQ= X-SBRS: 2.7 X-MesageID: 7892190 X-Ironport-Server: esa3.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.68,271,1569297600"; d="scan'208";a="7892190" From: Andrew Cooper To: Xen-devel Date: Tue, 5 Nov 2019 19:43:16 +0000 Message-ID: <20191105194317.16232-2-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20191105194317.16232-1-andrew.cooper3@citrix.com> References: <20191105194317.16232-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH 1/2] xen/livepatch: Add a return value to load hooks X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Andrew Cooper , Ross Lagerwall , Konrad Rzeszutek Wilk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) One use of load hooks is to perform a safety check of the system in its quiesced state. Any non-zero return value from a load hook will abort the apply attempt. Signed-off-by: Andrew Cooper Reviewed-by: Ross Lagerwall --- CC: Konrad Rzeszutek Wilk CC: Ross Lagerwall CC: Juergen Gross For several years, the following patch in the series has been shipped in ev= ery XenServer livepatch, implemented as a void load hook which modifies its ret= urn address to skip to the end of apply_payload(). This method is distinctly l= ess hacky. --- xen/common/livepatch.c | 30 +++++++++++++++++++----------- xen/include/xen/livepatch_payload.h | 2 +- xen/test/livepatch/xen_hello_world.c | 12 +++++++++--- 3 files changed, 29 insertions(+), 15 deletions(-) diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c index 7caa30c202..962647616a 100644 --- a/xen/common/livepatch.c +++ b/xen/common/livepatch.c @@ -1076,25 +1076,33 @@ static int apply_payload(struct payload *data) * temporarily disable the spin locks IRQ state checks. */ spin_debug_disable(); - for ( i =3D 0; i < data->n_load_funcs; i++ ) - data->load_funcs[i](); + for ( i =3D 0; !rc && i < data->n_load_funcs; i++ ) + rc =3D data->load_funcs[i](); spin_debug_enable(); =20 + if ( rc ) + printk(XENLOG_ERR LIVEPATCH "%s: load_funcs[%u] failed: %d\n", + data->name, i, rc); + ASSERT(!local_irq_is_enabled()); =20 - for ( i =3D 0; i < data->nfuncs; i++ ) - arch_livepatch_apply(&data->funcs[i]); + if ( !rc ) + for ( i =3D 0; i < data->nfuncs; i++ ) + arch_livepatch_apply(&data->funcs[i]); =20 arch_livepatch_revive(); =20 - /* - * We need RCU variant (which has barriers) in case we crash here. - * The applied_list is iterated by the trap code. - */ - list_add_tail_rcu(&data->applied_list, &applied_list); - register_virtual_region(&data->region); + if ( !rc ) + { + /* + * We need RCU variant (which has barriers) in case we crash here. + * The applied_list is iterated by the trap code. + */ + list_add_tail_rcu(&data->applied_list, &applied_list); + register_virtual_region(&data->region); + } =20 - return 0; + return rc; } =20 static int revert_payload(struct payload *data) diff --git a/xen/include/xen/livepatch_payload.h b/xen/include/xen/livepatc= h_payload.h index 4a1a96d054..3788b52ddf 100644 --- a/xen/include/xen/livepatch_payload.h +++ b/xen/include/xen/livepatch_payload.h @@ -9,7 +9,7 @@ * The following definitions are to be used in patches. They are taken * from kpatch. */ -typedef void livepatch_loadcall_t(void); +typedef int livepatch_loadcall_t(void); typedef void livepatch_unloadcall_t(void); =20 /* diff --git a/xen/test/livepatch/xen_hello_world.c b/xen/test/livepatch/xen_= hello_world.c index 02f3f85dc0..d720001f07 100644 --- a/xen/test/livepatch/xen_hello_world.c +++ b/xen/test/livepatch/xen_hello_world.c @@ -16,9 +16,11 @@ static const char hello_world_patch_this_fnc[] =3D "xen_= extra_version"; extern const char *xen_hello_world(void); static unsigned int cnt; =20 -static void apply_hook(void) +static int apply_hook(void) { printk(KERN_DEBUG "Hook executing.\n"); + + return 0; } =20 static void revert_hook(void) @@ -26,10 +28,14 @@ static void revert_hook(void) printk(KERN_DEBUG "Hook unloaded.\n"); } =20 -static void hi_func(void) +static int hi_func(void) { printk(KERN_DEBUG "%s: Hi! (called %u times)\n", __func__, ++cnt); + + return 0; }; +/* Safe to cast away the return value for this trivial case. */ +void (void_hi_func)(void) __attribute__((alias("hi_func"))); =20 static void check_fnc(void) { @@ -43,7 +49,7 @@ LIVEPATCH_UNLOAD_HOOK(revert_hook); /* Imbalance here. Two load and three unload. */ =20 LIVEPATCH_LOAD_HOOK(hi_func); -LIVEPATCH_UNLOAD_HOOK(hi_func); +LIVEPATCH_UNLOAD_HOOK(void_hi_func); =20 LIVEPATCH_UNLOAD_HOOK(check_fnc); =20 --=20 2.11.0 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel From nobody Fri Mar 29 05:11:09 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=none (zoho.com: 192.237.175.120 is neither permitted nor denied by domain of lists.xenproject.org) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=fail(p=none dis=none) header.from=citrix.com ARC-Seal: i=1; a=rsa-sha256; t=1572983088; cv=none; d=zoho.com; s=zohoarc; b=nAg7xsObHL0r5+MA7tMHG6Q6qlIL0NN+YPHCYhQoP7eDDU7Q05Fu53vkkik5mkVy/lQTZtcf4C4Nu5uiDY8RIG3TjiuuU2QQLO+cE4SH10nCDynPfxzIWH4re1gPaeEchFBpdqD7ZqMEhQ9t0LV3BqR2B6UxdH2OPTOccGP+9AI= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; 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d="scan'208";a="8392411" From: Andrew Cooper To: Xen-devel Date: Tue, 5 Nov 2019 19:43:17 +0000 Message-ID: <20191105194317.16232-3-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20191105194317.16232-1-andrew.cooper3@citrix.com> References: <20191105194317.16232-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH 2/2] x86/livepatch: Prevent patching with active waitqueues X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Andrew Cooper , Ross Lagerwall , Konrad Rzeszutek Wilk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) The safety of livepatching depends on every stack having been unwound, but there is one corner case where this is not true. The Sharing/Paging/Monitor infrastructure may use waitqueues, which copy the stack frame sideways and longjmp() to a different vcpu. This case is rare, and can be worked around by pausing the offending domain(s), waiting for their rings to drain, then performing a livepatch. In the case that there is an active waitqueue, fail the livepatch attempt w= ith -EBUSY, which is preforable to the fireworks which occur from trying to unw= ind the old stack frame at a later point. Signed-off-by: Andrew Cooper Reviewed-by: Konrad Rzeszutek Wilk Reviewed-by: Ross Lagerwall --- CC: Konrad Rzeszutek Wilk CC: Ross Lagerwall CC: Juergen Gross This fix wants backporting, and is long overdue for posting upstream. --- xen/arch/arm/livepatch.c | 5 +++++ xen/arch/x86/livepatch.c | 39 +++++++++++++++++++++++++++++++++++++++ xen/common/livepatch.c | 7 +++++++ xen/include/xen/livepatch.h | 1 + 4 files changed, 52 insertions(+) diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c index 00c5e2bc45..915e9d926a 100644 --- a/xen/arch/arm/livepatch.c +++ b/xen/arch/arm/livepatch.c @@ -18,6 +18,11 @@ =20 void *vmap_of_xen_text; =20 +int arch_livepatch_safety_check(void) +{ + return 0; +} + int arch_livepatch_quiesce(void) { mfn_t text_mfn; diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c index c82cf53b9e..0f129fa6b2 100644 --- a/xen/arch/x86/livepatch.c +++ b/xen/arch/x86/livepatch.c @@ -14,6 +14,45 @@ #include #include =20 +static bool has_active_waitqueue(const struct vm_event_domain *ved) +{ + /* ved may be xzalloc()'d without INIT_LIST_HEAD() yet. */ + return (ved && !list_head_is_null(&ved->wq.list) && + !list_empty(&ved->wq.list)); +} + +/* + * x86's implementation of waitqueue violates the livepatching safey princ= iple + * of having unwound every CPUs stack before modifying live content. + * + * Search through every domain and check that no vCPUs have an active + * waitqueue. + */ +int arch_livepatch_safety_check(void); +{ + struct domain *d; + + for_each_domain ( d ) + { +#ifdef CONFIG_MEM_SHARING + if ( has_active_waitqueue(d->vm_event_share) ) + goto fail; +#endif +#ifdef CONFIG_MEM_PAGING + if ( has_active_waitqueue(d->vm_event_paging) ) + goto fail; +#endif + if ( has_active_waitqueue(d->vm_event_monitor) ) + goto fail; + } + + return 0; + + fail: + printk(XENLOG_ERR LIVEPATCH "%pd found with active waitqueue\n", d); + return -EBUSY; +} + int arch_livepatch_quiesce(void) { /* Disable WP to allow changes to read-only pages. */ diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c index 962647616a..27ee5bdeb7 100644 --- a/xen/common/livepatch.c +++ b/xen/common/livepatch.c @@ -1060,6 +1060,13 @@ static int apply_payload(struct payload *data) unsigned int i; int rc; =20 + rc =3D apply_safety_checks(); + if ( rc ) + { + printk(XENLOG_ERR LIVEPATCH "%s: Safety checks failed\n", data->na= me); + return rc; + } + printk(XENLOG_INFO LIVEPATCH "%s: Applying %u functions\n", data->name, data->nfuncs); =20 diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h index 1b1817ca0d..69ede75d20 100644 --- a/xen/include/xen/livepatch.h +++ b/xen/include/xen/livepatch.h @@ -104,6 +104,7 @@ static inline int livepatch_verify_distance(const struc= t livepatch_func *func) * These functions are called around the critical region patching live cod= e, * for an architecture to take make appropratie global state adjustments. */ +int arch_livepatch_safety_check(void); int arch_livepatch_quiesce(void); void arch_livepatch_revive(void); =20 --=20 2.11.0 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel