From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794591277; b=K1uFfUiOLJZI4EqLlQ0h3OVxMwfuT+3U/98HTI+G4+ErAt83mdOVGSaa7ErBkVsigGBJ thQBKpMyxLwHWuk2GfBtZUG8jpYQSeQo5WneeOjMFCfE5UEtPmusRPuj1GP5Ju6X2108f uFxGOjWVV0xKuHX51iPHQLhJ6lC2Fmm4PUKviqz95mvyUmvQym84t+2xxrIIAt7ScH+bq xq8JWHkFr8wKy5RajMzLokFKJmuSQTsKLusiajJi/sEXb1AVTkGRAsXowb0VCBrXJyPJf YaI+TEO4CiTwt7KpT0ObS+qQbsnpFsKUOy7R5WI5xE4ZhZUX7CwkKnblYGS/18R0zeg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794591277; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=wAaEF+00zyJBpfZu2q2HCKKN+7uai37GR1Wv/fu32oI=; b=LC20NqsQ0CfA2XYQ7CWnjrm5ohdZkPYcxDIyIIkxEynY5CagYZkgTB36rBusHF2nzN5G DmNO1wXO/XNQ7/e7H/MpCi/yK++7jdVEBNng8vwf2SeiGN+JJtsbhPlJnXZPdVadqGuoQ YBNTYjD42n4G+uiPmNH3GUG7IwqKXc+UFOf/iKytRoP5kJQRQybeK5kfeqE3pEZMB4YcT CkbikE+YdzVZlgvW2JhjjrxG9eRe4b1pMrLPXJmq1hILI80hSD1R8HAAflhzhoWFOXgjQ zYyyguABFQD7Cu1BRbytX26s7JOIoOIp6eVs306ps9Xd/ZpMlEsfqY2PMUOsnS+6mCw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=Lir5+0oG; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C3B426076FBD; Fri, 13 Nov 2026 17:34:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=Lir5+0oG Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F1C31F000C4; Fri, 13 Nov 2026 17:34:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794591277; bh=wAaEF+00zyJBpfZu2q2HCKKN+7uai37GR1Wv/fu32oI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Lir5+0oGuG0Ijt0MT5EdnyMRhMUmIuO77ip/EtGPfFmP19vSZ4YKt+0OnM0uI3wSZ CA8Cd2LJwZMf90qB9z8+D4FiKx4FgzbNLzb2E8MzwpU0OxeDMbRwnD1A3K/WJXfzP7 NaprqO+qMNW6nQIMzzFmGQ7SlabjFkDyvO2ZTH+4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Kiryl Shutsemau (Meta)" , Breno Leitao , Catalin Marinas , Sasha Levin Subject: [PATCH 6.12 399/670] arm64: sdei: Preserve the interrupted contexts exception registers Date: Fri, 13 Nov 2026 10:49:23 -0500 Message-ID: <20261113153825.276360843@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kiryl Shutsemau (Meta) [ Upstream commit 58c1eb84e97701c583605ba2fd553b69afba2245 ] An SDEI event is dispatched by firmware regardless of PSTATE.DAIF, so it can interrupt the kernel where the exception registers are live: - exception entry, before kernel_entry has saved ELR_EL1/SPSR_EL1 and before the C handler has read ESR_EL1/FAR_EL1; - exception return, after kernel_exit has loaded ELR_EL1/SPSR_EL1 and before the ERET. An IRQ or pseudo-NMI cannot arrive there with PSTATE.I set. Firmware saves only x0-x17, PC and PSTATE around an SDEI event, so a synchronous exception taken by the handler overwrites the interrupted context's ELR, SPSR, ESR and FAR. do_sdei_event() only notices that ELR changed, and warns. The interrupted context then carries on with the handler's state. A task interrupted on its way into the kernel can be sent SIGILL for the handler's kernel data abort. A task interrupted on its way back to user space ERETs to EL1, at the handler's fixup address, with user registers loaded. With SDEI delivering NMI backtraces, this happens in normal operation. The handler runs show_regs(), which reads through possibly-NULL pointers with the _nofault() accessors. print_worker_info() faults this way for a kworker that is not running a work item, and a single sysrq-l warned once per such kworker. Save ELR, SPSR, ESR and FAR in __sdei_handler() before irqentry_nmi_enter(), which can take an exception too, and restore them after irqentry_nmi_exit(). Once they are restored, a nested exception is harmless if its handler is safe in NMI context. That holds for EL1 data aborts on translation, permission and access-flag faults, which never take the mmap lock in NMI context, and for BRK. Warn once, with the syndrome, about any other exception class. Fixes: f5df26961853 ("arm64: kernel: Add arch-specific SDEI entry code and CPU masking") Cc: stable@vger.kernel.org Signed-off-by: Kiryl Shutsemau (Meta) Tested-by: Breno Leitao Signed-off-by: Catalin Marinas [ kas: keep arm64_enter_nmi()/arm64_exit_nmi() in __sdei_handler() ] Signed-off-by: Kiryl Shutsemau (Meta) Signed-off-by: Sasha Levin --- arch/arm64/kernel/entry-common.c | 21 ++++++++++++- arch/arm64/kernel/sdei.c | 53 ++++++++++++++++++++++++++------ 2 files changed, 64 insertions(+), 10 deletions(-) diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 8539e75a2b7ea..4033ee7005a4a 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -1088,7 +1088,7 @@ asmlinkage void noinstr __noreturn handle_bad_stack(struct pt_regs *regs) asmlinkage noinstr unsigned long __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg) { - unsigned long vbar; + unsigned long elr, spsr, esr, far, vbar; unsigned long ret; /* @@ -1113,6 +1113,17 @@ __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg) else if (cpu_has_pan()) set_pstate_pan(0); + /* + * Nothing saved the interrupted context's exception registers on the + * way in, and it may be in the middle of exception entry or return + * (SDEI ignores DAIF). Save them before anything can take an exception + * and overwrite them. + */ + elr = read_sysreg(elr_el1); + spsr = read_sysreg(spsr_el1); + esr = read_sysreg(esr_el1); + far = read_sysreg(far_el1); + /* * With KPTI, VBAR_EL1 holds the trampoline vectors from the return to * EL0 until the next exception from EL0 maps the kernel. They only @@ -1132,6 +1143,14 @@ __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg) ret = do_sdei_event(regs, arg, vbar); arm64_exit_nmi(regs); + /* + * Put them back unconditionally. An unchanged ELR does not rule out a + * nested exception: one may have returned to the same address. + */ + write_sysreg(elr, elr_el1); + write_sysreg(spsr, spsr_el1); + write_sysreg(esr, esr_el1); + write_sysreg(far, far_el1); write_sysreg(vbar, vbar_el1); return ret; diff --git a/arch/arm64/kernel/sdei.c b/arch/arm64/kernel/sdei.c index c867baa9f9f64..a6d78ceb1364d 100644 --- a/arch/arm64/kernel/sdei.c +++ b/arch/arm64/kernel/sdei.c @@ -203,6 +203,31 @@ unsigned long sdei_arch_get_entry_point(int conduit) return 0; } +/* + * Exceptions an SDEI handler may take without harm once __sdei_handler() has + * restored the interrupted context's exception registers. Their handlers are + * safe in NMI context: + * - EL1 data aborts on translation, permission and access-flag faults: + * faulthandler_disabled() is true in NMI context, so do_page_fault() never + * takes the mmap lock. This covers the _nofault() accessors used by the + * generic dump_stack()/show_regs() code (e.g. print_worker_info()). + * - BRK: kprobes, WARN/BUG, kCFI and UBSAN traps, all NMI-capable. + * Anything else taken at EL1 is fatal on its own, or unexpected here. + */ +static bool sdei_nested_exception_ok(unsigned long esr) +{ + switch (ESR_ELx_EC(esr)) { + case ESR_ELx_EC_DABT_CUR: + return esr_fsc_is_translation_fault(esr) || + esr_fsc_is_permission_fault(esr) || + esr_fsc_is_access_flag_fault(esr); + case ESR_ELx_EC_BRK64: + return true; + default: + return false; + } +} + /* * do_sdei_event() returns one of: * SDEI_EV_HANDLED - success, return to the interrupted context. @@ -219,6 +244,7 @@ unsigned long __kprobes do_sdei_event(struct pt_regs *regs, int i, err = 0; int clobbered_registers = 4; u64 elr = read_sysreg(elr_el1); + u64 nested_elr, nested_esr, nested_far; u32 kernel_mode = read_sysreg(CurrentEL) | 1; /* +SPSel */ if (arm64_kernel_unmapped_at_el0()) @@ -231,18 +257,27 @@ unsigned long __kprobes do_sdei_event(struct pt_regs *regs, } err = sdei_event_handler(regs, arg); - if (err) - return SDEI_EV_FAILED; - if (elr != read_sysreg(elr_el1)) { - /* - * We took a synchronous exception from the SDEI handler. - * This could deadlock, and if you interrupt KVM it will - * hyp-panic instead. - */ - pr_warn("unsafe: exception during handler\n"); + /* + * A synchronous exception taken by the handler has overwritten the + * exception registers; __sdei_handler() puts them back. Only the last + * one's syndrome survives; report it if it is not one known to be + * harmless. + * + * If the event interrupted a KVM world switch, VBAR points at the KVM + * hyp vectors and any such exception is a hyp panic instead. + */ + nested_elr = read_sysreg(elr_el1); + nested_esr = read_sysreg(esr_el1); + nested_far = read_sysreg(far_el1); + if (nested_elr != elr && !sdei_nested_exception_ok(nested_esr)) { + pr_warn_once("unexpected exception during handler: ESR %#llx FAR %#llx near %pS\n", + nested_esr, nested_far, (void *)nested_elr); } + if (err) + return SDEI_EV_FAILED; + mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK); /* -- 2.53.0