From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5A203C369C2 for ; Fri, 25 Apr 2025 16:22:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:References:Message-ID:Subject:Cc:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ujk3/IGYnXx3Wxmgegzw/+bFfTW+UygvpTNGj7Kcyas=; b=LzBmbl3o0fFCiGgnAYaIZC5X/X VxCpYoPc71DboXow4Q2poeDXzddYGdOJ+we5DNI0jusVZPcMBkosd1ks0CgR7U18qakrsfOuAB+8a YGsFA++aRlVJK303qlrFTq6Tzgnuk8kYEH3aEduU5DmqelHACQ3aJ5lMlSO8vRUw/Lk3exPTPpKK+ AzScuyOTXIMCmEi59QSLJTrgZ/J4zlDJti/5IGugDQkKp/TTY4UGakseFiSE/tjr+0osz8TZEgxOe gjtMPMoUFuUSIkKuteyemNIHmV4OLz2JlR3BRAhAJJsao2due3VrYvnmJAW77U1SYuXbhVPaoPMIY gqxUOOmQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1u8LpC-00000000Bue-1rIe; Fri, 25 Apr 2025 16:22:50 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1u8KBK-0000000HSje-2g4d for linux-arm-kernel@lists.infradead.org; Fri, 25 Apr 2025 14:37:37 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1745591852; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ujk3/IGYnXx3Wxmgegzw/+bFfTW+UygvpTNGj7Kcyas=; b=fHdvbbkRnuAcHV9Ff2u63X4GfbPxUpdnRy9sJTjJLPaT2o7f1t76EuUJ/YGVRS0ccZQ48y ABI94Km6CDY2KnVZaZWMMNRHiEEUxRrejFxoKhMzKgm5vLGjX1VvHhSs9/qfgiYgQqobWi b5nMGD7FOSrPovktSzpepe2iGYwP4QY= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-251-Vuvsb1rGNWOVF8Kn-8giVg-1; Fri, 25 Apr 2025 10:37:28 -0400 X-MC-Unique: Vuvsb1rGNWOVF8Kn-8giVg-1 X-Mimecast-MFC-AGG-ID: Vuvsb1rGNWOVF8Kn-8giVg_1745591848 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-39ef89b862dso1216434f8f.0 for ; Fri, 25 Apr 2025 07:37:28 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1745591847; x=1746196647; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=Ujk3/IGYnXx3Wxmgegzw/+bFfTW+UygvpTNGj7Kcyas=; b=p5MjaqzFF7nt6BzKc1PB2o9YiGNJUvbtiQDd0+uzfwVSRYcjxUv6YCBsMZzxiaaa+X Dd4SnS4hpFYS4qTYhIQPK5zJFvOmvTSCr0rE3W2InrYyx7ZVG9Gm+p0M60G9ZIxRfUW2 nOEWNXn8u7l14QUzYPSPKhXZF84XRdC+RPq4hgiFqu2FxYlPXYyTmH40kNhFfSp6pMRa 8vs272NMhCa2w0dgNfbw0FWXDD3z8tK8eyjWpGDy+9AEDGCsbDWsXfBNGNF0OANj6J6P KHh2rV2xunzBWd0JlmG3F0srwIUDwEO5eOvtdVLupt6kUV1Irzb40AwxrDlqQr0GkolA BO2Q== X-Forwarded-Encrypted: i=1; AJvYcCViQWDPR1BCh6j7WZEVqUmXQfs9y4h6Q1BcfD3iO24VYW3MsXmMdD+HOajAdvwpZTvuHuCwtsNVAoBXpf0YrRSH@lists.infradead.org X-Gm-Message-State: AOJu0Yyb3TaKOfzNdBMDLcLEYi6IBT8yErYXsnum+VXv3xeh8/yvehSm SL3Lfwe1vr0fGMqFj+IAUvOT5X27iwuO0Kgm6Axy1a6zrkolFns6LkgbwceGwhQjpSUEcrs9qMA xYQZ8GdfqGePsvO0YU4J9T3Z3/6rgNeQJ4nsJhn7hqSxGrszkJiodQUq9IAaaz0ui9y2o0Chv X-Gm-Gg: ASbGncuU/DeKF/omwlrw4epA1CQ9jR8HQ3GyshA871g8P7uQ3F1J+hOWFMWCn2Eb8vw ig6gDbYr4ycayxnZKHKPT7C/VRn5S6cxePpxNZPXNB9VSYGxpEXbNN//riT5Pno/Dva4qH82KIM iLt/Xy5sgmYhzruN6T2vx0xtVO5RC92Ju5hi52HAM6Wwc15yD0oIeFA/Y6RSeP9PUnruA93GnP7 1BRfL93aqkpnrwmmrk0TItz0YQEMm3bPOvk1BJ1UJ2Kn3N6g/xNWZLqIq5gv6UY4ODxMvIjNsI4 fm4qFwkLOAn/t+ot99p2p0Xrug== X-Received: by 2002:a5d:47ad:0:b0:39e:cbca:8a4b with SMTP id ffacd0b85a97d-3a074e0e1a8mr2130260f8f.6.1745591847598; Fri, 25 Apr 2025 07:37:27 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHHQ8vRI/X7PrO43k0DiFqkqa4Uk8XRAM7d2gJ9xafb1xfkOT7jJlK6mrbxxsPSXHf+XLM2Jg== X-Received: by 2002:a5d:47ad:0:b0:39e:cbca:8a4b with SMTP id ffacd0b85a97d-3a074e0e1a8mr2130242f8f.6.1745591847204; Fri, 25 Apr 2025 07:37:27 -0700 (PDT) Received: from t14ultra (109-81-82-22.rct.o2.cz. [109.81.82.22]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-440a530a6e9sm26807935e9.16.2025.04.25.07.37.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Apr 2025 07:37:26 -0700 (PDT) Date: Fri, 25 Apr 2025 16:37:47 +0200 From: Jan Stancek To: Thomas =?iso-8859-1?Q?Wei=DFschuh?= Cc: Andy Lutomirski , Thomas Gleixner , Vincenzo Frascino , Catalin Marinas , Will Deacon , Anna-Maria Behnsen , Frederic Weisbecker , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Arnd Bergmann , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, Nam Cao Subject: Re: [PATCH 08/19] vdso/gettimeofday: Prepare do_hres_timens() for introduction of struct vdso_clock Message-ID: References: <20250303-vdso-clock-v1-0-c1b5c69a166f@linutronix.de> <20250303-vdso-clock-v1-8-c1b5c69a166f@linutronix.de> <20250424173908-ffca1ea2-e292-4df3-9391-24bfdaab33e7@linutronix.de> <20250425104552-07539a73-8f56-44d2-97a2-e224c567a2fc@linutronix.de> <20250425152733-0ff10421-b716-4a55-9b60-cb0a71769e56@linutronix.de> MIME-Version: 1.0 In-Reply-To: <20250425152733-0ff10421-b716-4a55-9b60-cb0a71769e56@linutronix.de> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 9R9y46S3q7vVMujR4QT21orCCG-KvX-2GzQt4tLXx3Y_1745591848 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250425_073734_757281_3B93F018 X-CRM114-Status: GOOD ( 16.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Apr 25, 2025 at 03:40:55PM +0200, Thomas Weißschuh wrote: > >Some more information: > >The crash comes from the address arithmetic in "vc = &vc[CS_RAW]" going wrong. That appears to be because it's not doing any arithmetic, but using value from some linker-generated symbol (I'll refer to it as "7a8"). The below is presumably the check that compares clk != CLOCK_MONOTONIC_RAW, CLOCK_MONOTONIC_RAW is 4. And it should choose between first and second vdso_clock in 2nd vvar page: # readelf -a /root/kernel-ark/arch/arm64/kernel/vdso/vdso.so.dbg | grep 7a8 25: 00000000000007a8 0 NOTYPE LOCAL DEFAULT 7 $d objdump -d -S: 658: 17ffffef b 614 <__cvdso_clock_gettime_data.constprop.0+0x104> vc = &vc[CS_HRES_COARSE]; 65c: 58000a62 ldr x2, 7a8 <__cvdso_clock_gettime_data.constprop.0+0x298> 660: 7100101f cmp w0, #0x4 664: 10e7cce3 adr x3, fffffffffffd0000 668: 9a821063 csel x3, x3, x2, ne // ne = any while (unlikely((seq = READ_ONCE(vc->seq)) & 1)) 66c: b9400065 ldr w5, [x3] ... 7a8: fffd00e0 .word 0xfffd00e0 7ac: ffffffff .word 0xffffffff (gdb) r Thread 2.1 "a.out" received signal SIGSEGV, Segmentation fault. [Switching to Thread 0xfffff7ff2dc0 (LWP 44638)] 0x0000fffff7fa066c in ?? () (gdb) disassemble 0x0000fffff7fa0658,0x0000fffff7fa067c --Type for more, q to quit, c to continue without paging-- 0x0000fffff7fa0658: b 0xfffff7fa0614 0x0000fffff7fa065c: ldr x2, 0xfffff7fa07a8 0x0000fffff7fa0660: cmp w0, #0x4 0x0000fffff7fa0664: adr x3, 0xfffff7f70000 0x0000fffff7fa0668: csel x3, x3, x2, ne // ne = any => 0x0000fffff7fa066c: ldr w5, [x3] $x3 here is using correct vvar runtime address, but $x2 uses a bogus one from "7a8". And when it tries to load from it, it crashes: (gdb) info proc map process 44638 Mapped address spaces: Start Addr End Addr Size Offset Perms File 0x0000000000400000 0x0000000000410000 0x10000 0x0 r-xp /root/ltp/testcases/kernel/syscalls/clock_gettime/a.out 0x0000000000410000 0x0000000000420000 0x10000 0x0 r--p /root/ltp/testcases/kernel/syscalls/clock_gettime/a.out 0x0000000000420000 0x0000000000430000 0x10000 0x10000 rw-p /root/ltp/testcases/kernel/syscalls/clock_gettime/a.out 0x0000fffff7d80000 0x0000fffff7f30000 0x1b0000 0x0 r-xp /usr/lib64/libc.so.6 0x0000fffff7f30000 0x0000fffff7f40000 0x10000 0x1a0000 r--p /usr/lib64/libc.so.6 0x0000fffff7f40000 0x0000fffff7f50000 0x10000 0x1b0000 rw-p /usr/lib64/libc.so.6 0x0000fffff7f60000 0x0000fffff7fa0000 0x40000 0x0 r--p [vvar] 0x0000fffff7fa0000 0x0000fffff7fb0000 0x10000 0x0 r-xp [vdso] 0x0000fffff7fb0000 0x0000fffff7fe0000 0x30000 0x0 r-xp /usr/lib/ld-linux-aarch64.so.1 0x0000fffff7fe0000 0x0000fffff7ff0000 0x10000 0x20000 r--p /usr/lib/ld-linux-aarch64.so.1 0x0000fffff7ff0000 0x0000fffff8000000 0x10000 0x30000 rw-p /usr/lib/ld-linux-aarch64.so.1 0x0000fffffffd0000 0x0001000000000000 0x30000 0x0 rw-p [stack] $x3 was the beginning of 2nd vvar page (1st vdso_clock), and $x2 looks like it should have been 2nd vdso_clock, but the value that is used is not the address of vvar during runtime. vdso_clock has size 224 == 0xe0 (according to pahole) (gdb) x/2x 0xfffff7fa07a8 0xfffff7fa07a8: 0xfffd00e0 0xffffffff (gdb) p/x $x2 $1 = 0xfffffffffffd00e0 (gdb) x/1x $x2 0xfffffffffffd00e0: Cannot access memory at address 0xfffffffffffd00e0 But it does match the symbol value from vdso.so: # readelf -a /root/kernel-ark/arch/arm64/kernel/vdso/vdso.so.dbg | grep vdso_u 37: fffffffffffc0000 0 NOTYPE LOCAL DEFAULT 1 vdso_u_data 39: fffffffffffc0000 0 NOTYPE LOCAL DEFAULT ABS vdso_u_time_data 40: fffffffffffe0000 0 NOTYPE LOCAL DEFAULT ABS vdso_u_rng_data >>> print(hex(0xfffffffffffc0000+65536+224)) 0xfffffffffffd00e0 -> and this is address where it crashes Regards, Jan >This should just do "vc = vc + 1", advancing the pointer by sizeof(*vc). >But I get these example values of "vc" before and after the arithmetic: >0x00ffffbc060000 -> 0xfffffffffffd00e8 >Which is obviously wrong. > >The arithmetic can be fixed with any one of the following changes: >* OPTIMIZER_HIDE_VAR() as above >* Replacement of -mcmodel=tiny with -mcmode=small in arch/arm64/kernel/vdso/Makefile > -mcmodel=tiny is supposed to cover 1MiB programs, the vDSO only needs 300KiB here >* Removal of the (clk != CLOCK_MONOTONIC_RAW) case > >Shuffling code around, even without any impact on semantics, sometimes fixes >the issue. Compiling the vDSO with UBSAN didn't show anything. > > >Thomas > >> > > > > [1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/clock_gettime/clock_gettime03.c >> > > > > [2] https://koji.fedoraproject.org/koji/buildinfo?buildID=2704401 >> > > > >> > >> >