From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D10ED1632DD for ; Mon, 5 Oct 2026 22:17:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791238655; cv=none; b=Ke3kmIJHC+o5nxzUozfS9/rnS8G9knNhbLy6YPmvG6huHoue32AP5mjcmlw/KVPOWyDGELvMdTZARGyLP5naNDXMOHV+Pbx6oEyNQVS6KJIn1CuR94LG1qy2B26ZfHs1sFV/Tf+c7CdOzjVNEpGi57cks/R7vXIKfjk3sh4fsY4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791238655; c=relaxed/simple; bh=HtlWRYVx55XPFHLaXNC15T5DQTTXKW1alDum9H22kq4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GqYY/fJ3Ngm1wsfgq8dKtV/ybjZmF4go7Wc6A3y2lJpbJR1QBslTv6iqgEqnwx+Qsg7A1s+x5brPD3Q9UkGXDLRtAbWlgmvLmgB67PLaY+aLZGy0qwQZyulV995XXk3CuYNB784Bw4Qber55K9LG6u4iEfkaopwCXexCP418x3I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UD7p8ty/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UD7p8ty/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F34E41F000FF; Mon, 5 Oct 2026 22:17:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791238653; bh=ay/hSsIOHUUHzoqB4jU5UFFQOkfAQ5cWtSi7HWbeayY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=UD7p8ty/AhRW0Lj8hFPhvbUox3Njmn3rCR3mwFZTM25xe0aIloUU4CVa36RfumceT LAFFTiGl9VP3OGGtk1AfbpLTywOGumaq3Eb7hMHrcZi5IRsqz5OGAc5oufbs6Gufmb uCLcRVHcT3sH+k7LJ3ve3XJbsywnIrmEtrrZdn6ZkQkvNoqzFG+bUrUuppFjw5TKbd 1LGqFVhavbuuI9KJj1y/Vb9W5X2cKk290kr5ufjF7qs5br8fkPsvkN2nMkUpOkgSZT puYYTkQBMqpOlgf4FR8Jwi5mPfi/bDsZVPRqL+daozsHro66rFU7svP+YL0pJD+Ogt e8CdWdDAx5Qzg== From: Sasha Levin To: stable@vger.kernel.org Cc: Mark Rutland , Mark Brown , Catalin Marinas , Will Deacon , Sasha Levin Subject: [PATCH 6.12.y 2/2] arm64/fpsimd: signal: Forbid non-streaming SVE payload on SME-only systems Date: Mon, 5 Oct 2026 18:17:27 -0400 Message-ID: <20261005221636.3436132-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261005221636.3436132-1-sashal@kernel.org> References: <2026100534-amigo-discolor-973f@gregkh> <20261005221636.3436132-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Mark Rutland [ Upstream commit e060d9069b49fe55f38057dfe592068014652671 ] When system_supports_sme() is true but system_supports_sve() is false, restoring a specifically crafted SVE signal context can result in the task erroneously having non-streaming SVE state. Subsequent attempts to manipulate the task's FPSIMD/SVE/SME state can result in a variety of problems, including fatal EL1 UNDEFs. In such configurations, the kernel always creates an SVE signal context when delivering a signal, and this can only be in one of two states: (1) SVE_SIG_FLAG_SM is set, and an SVE payload is present containing streaming mode SVE state. The recorded VL is the task's live streaming VL. (2) SVE_SIG_FLAG_SM is clear, and an SVE payload is not present. The FPSIMD context contains the non-streaming mode FPSIMD state. The recorded VL is 0. Currently restore_sve_fpsimd_context() correctly rejects cases where SVE_SIG_FLAG_SM is set and an SVE payload is not present, but fails to reject cases where SVE_SIG_FLAG_SM is clear and an SVE payload is present. Consequently, restore_sve_fpsimd_context() can place the task in a state where it has non-streaming SVE state even when this is not supported by HW. For example, this can cause a later EL1 UNDEF when the kernel attempts to restore the task's ZCR_EL1 value: | # ./sme-sigcontext-to-sve | Internal error: Oops - Undefined instruction: 0000000002000000 [#1] SMP | Modules linked in: | CPU: 0 UID: 0 PID: 131 Comm: sme-sigcontext- Not tainted 7.3.0-rc1 #1 PREEMPT | Hardware name: linux,dummy-virt (DT) | pstate: 61402009 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) | pc : fpsimd_restore_current_state+0x258/0x458 | lr : exit_to_user_mode_loop+0xb8/0x188 | sp : ffff80008056be40 | x29: ffff80008056be40 x28: fff00000c1670000 x27: 0000000000000000 | x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 | x23: ffff80008056bec0 x22: 0000000000000008 x21: 0000000000000040 | x20: 0000000000000081 x19: 0000000008800010 x18: 0000000000000000 | x17: 0000fffffd412570 x16: 0000000000001000 x15: 0000fffffd4123b0 | x14: 0000fffffd412780 x13: 0000fffffd412be8 x12: 0000000047435300 | x11: 0000fffffd412570 x10: 0000000000000000 x9 : 0000000045585401 | x8 : fff00000c18a6c44 x7 : 0000000000000000 x6 : 0000000000000002 | x5 : 0000000000000002 x4 : ffff800080568000 x3 : 0000000000000001 | x2 : 0000000008800010 x1 : fff00000c1670000 x0 : 0000000008800000 | Call trace: | fpsimd_restore_current_state+0x258/0x458 (P) | exit_to_user_mode_loop+0xb8/0x188 | el0_svc+0x1cc/0x1d0 | el0t_64_sync_handler+0xa0/0xe4 | el0t_64_sync+0x198/0x19c | Code: d5384101 f9400020 53175c03 36b80de0 (d5381202) | ---[ end trace 0000000000000000 ]--- | Kernel panic - not syncing: Oops - Undefined instruction: Fatal exception in interrupt | Kernel Offset: 0x291fb1000000 from 0xffff800080000000 | PHYS_OFFSET: 0x40000000 | CPU features: 0x0,00000000,0052802f,ffb88f43,3afcf73f | Memory Limit: none Rework restore_sve_fpsimd_context() to reject cases where SVE_SIG_FLAG_SM is clear and an SVE payload is not present. As parse_user_sigframe() rejects SVE signal frames when neither SVE nor SME are supported, it isn't necessary for restore_sve_fpsimd_context() to handle the case where neither are supported. Fixes: 7dde62f0687c ("arm64/signal: Always accept SVE signal frames on SME only systems") Signed-off-by: Mark Rutland Reviewed-by: Mark Brown Cc: Catalin Marinas Cc: Will Deacon Cc: stable@vger.kernel.org Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- arch/arm64/kernel/signal.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 59d9e7fca936a..13f4a95ca2315 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -392,6 +392,7 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user) unsigned int vl, vq; struct user_fpsimd_state fpsimd; u16 user_vl, flags; + bool fpsimd_only; bool sm; if (user->sve_size < sizeof(*user->sve)) @@ -402,19 +403,33 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user) if (err) return err; + fpsimd_only = (user->sve_size == sizeof(*user->sve)); sm = flags & SVE_SIG_FLAG_SM; + if (sm) { if (!system_supports_sme()) return -EINVAL; + /* + * Streaming SVE state is always preserved with an SVE payload. + * Only accept streaming state which has an SVE payload. + */ + if (fpsimd_only) + return -EINVAL; + vl = task_get_sme_vl(current); } else { /* - * A SME only system use SVE for streaming mode so can - * have a SVE formatted context with a zero VL and no - * payload data. + * Non-streaming SVE state may be preserved without an SVE + * payload, in which case all state is saved in the FPSIMD + * context. + * + * On SME-only systems, non-streaming (FPSIMD-only) state is + * always preserved without an SVE payload, and with VL==0. On + * such systems, only accept non-streaming state without an SVE + * payload. */ - if (!system_supports_sve() && !system_supports_sme()) + if (!system_supports_sve() && !fpsimd_only) return -EINVAL; vl = task_get_sve_vl(current); @@ -423,16 +438,7 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user) if (user_vl != vl) return -EINVAL; - /* - * Non-streaming SVE state may be preserved without an SVE payload, in - * which case the SVE context only has a header with VL==0, and all - * state can be restored from the FPSIMD context. - * - * Streaming SVE state is always preserved with an SVE payload. For - * consistency and robustness, reject restoring streaming SVE state - * without an SVE payload. - */ - if (!sm && user->sve_size == sizeof(*user->sve)) + if (fpsimd_only) return restore_fpsimd_context(user); vq = sve_vq_from_vl(vl); -- 2.53.0