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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 E1B29C369C2 for ; Fri, 25 Apr 2025 14:37:40 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Zkb6C3mq9z2ytV; Sat, 26 Apr 2025 00:37:39 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1745591859; cv=none; b=UScYTU0JN9zEs03Wld1yXRdxtvmXVw83i4Huib+pNzy5SqDGtI/Xf6tI/VEC2DNt6TEU7BLtoSmbl485v8aKIv8+Ns42Ay1ShHe5+M2ooLymQ4Ad+p6bbOn6EUUaih1MJUXTm42+KIeqx2Ult+lzBt+lmyiJuiWTlgyNsYjIxJhg4H2WvVkhs/VGTx7ecLHR10SoeWyJpxovA/pVENb4SO4C8v4iKu75YahTonS5tTge44qjMq062SSH+8GjSJShs4CWZTzknXWYYXQWhG0xSMCslwDvrJYGwTUTsxM/0ZfniCnPeCPtfaSrNvBQYN/shh6tbCIj0wQaRTbli2+gnA== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1745591859; c=relaxed/relaxed; bh=Ujk3/IGYnXx3Wxmgegzw/+bFfTW+UygvpTNGj7Kcyas=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: In-Reply-To:Content-Type:Content-Disposition; b=MIJ4sc6sDfCx3sIK81zXzLoZTnlq9v1qhp5RwI7b/gzLBDTZJevTxryn6LpTe17udbGdvzUITB6kfwuwJUnKFUuzn6jtC46B1POevflYSwKoh5SrWawsx4dCgX1/yBKiUDu6Fm6vKfdoyv2NnoBkqX1XT27mHUf4M02i+2FAAk0gh5Hgo0X5w/RIDocSvBWCXLNyIr/S/hCckxAQ1wzcNLpR0vHMtKsi1W2witoASTLZ3R6+86yzFyr8ZLuiPF1staROE/l6A7JkFYgx/xbShUejY3tW8RxLmUtUCUCD+tyRfljpwYAc7lsKIdfT9hMFFeKU35cUrUrcxOmi3EvTsg== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=fHdvbbkR; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=DQ9+0aEs; dkim-atps=neutral; spf=pass (client-ip=170.10.129.124; helo=us-smtp-delivery-124.mimecast.com; envelope-from=jstancek@redhat.com; receiver=lists.ozlabs.org) smtp.mailfrom=redhat.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=fHdvbbkR; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=DQ9+0aEs; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=redhat.com (client-ip=170.10.129.124; helo=us-smtp-delivery-124.mimecast.com; envelope-from=jstancek@redhat.com; receiver=lists.ozlabs.org) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Zkb695vr1z2yrt for ; Sat, 26 Apr 2025 00:37:35 +1000 (AEST) 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= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1745591853; 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=DQ9+0aEsSIxBAwN0NHKmJTBjMC/QY0VdkWkjo8/gM70eXPFBFeOjZX8qZyvmVZZoUjycP5 +B4O8pxU7g1aG9+9Pb7qrfakBF5jL4xbcfctTI9SgAR1U3VW/qb2LNJ1URn3B2B6gsH/Kd ykoDQhexwvT4XNjZeuoxXPvY/BEzmFc= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-299-giXxFahTMwCNGAcmkwD27A-1; Fri, 25 Apr 2025 10:37:28 -0400 X-MC-Unique: giXxFahTMwCNGAcmkwD27A-1 X-Mimecast-MFC-AGG-ID: giXxFahTMwCNGAcmkwD27A_1745591848 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-39ac9b0cb6aso1065377f8f.2 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=GJo3XkI3S5i9nFiwnIWunNqxwKOkhlV7BD32xcOiWjUMv2QULPcoQi/wTAJaj1quAY YEM3vtCl9zkMYefc+gEOVIi3s+T42iOiC1fVehD+Ol8R4KWN+z8sGbLZ+U29aRhNNU00 DYHDlkHT4CoJZJRH2SWxZSYOjX9r6b9q6eP1MdRVbtmIS3NynRFXnpc/qk1+xygj7D2x 1Ap9c9RnBJuXZdAMF1eeNK9sYtuEzJ6/QnkZf4c+UGz4FbMevL1NSVkcZunFXuHQSWaC 5Pfou/vXCbnVkua1/72kRZ65HVzsqM38uhMJSLOJJ0TzPm4xnO02q+lTWrLBpseWpQBu cbxw== X-Forwarded-Encrypted: i=1; AJvYcCUftNHkF9gEj7wlhr1s60jkzb7Shb+2ggsuvYeGj5WYaKybbne5Mt3MUyxItep0MLnrNwrOo0q1Vtviees=@lists.ozlabs.org X-Gm-Message-State: AOJu0Yyq2RHFnYKIxTs+8dAdhCOPJ+he54AZ42J8XOmOq2EyjwK8/4hb RGF0kvlMzJsRHahvsXNSP5hC8wNhYrXO86E+wDTaWJH8GmnTHMBJap+kQ9gfMM/A9V0CPBBVF0m PKEDwDo7jhRNvDoSn/4jWsLX2e+Z7i9MAZpDGYniqfp+5IQIhUZOeDxG+1RGfldo= X-Gm-Gg: ASbGncu6ymQUmo1A17nnrqo7SWJN+210zcAfRslq6eZDckwlzW+N4VA/UJVmq/vclDD 5KN2/PgMzf2r9QJC6qSA2ir41/GRjbwfYjNMOn1g/GjkviXuB7V0HjV4ZLoTL0d75nhFopLfemC mXZ/YJIgnQKlKC9xk3Rt6QOv0AKTh/8UBCnkVQYwODStHgeLZHJ0lwnqy547pJ3A2WnDAILJzJA TLMjuoYFDisuKjzD5Zld4ghdciUzQCBIc38sGXpq26w5oZEPaB9MoPe5B9Y4JK1tBcT2hLq/g3l lCLrZH0STpSpDRTEkBPK3pEnag== X-Received: by 2002:a5d:47ad:0:b0:39e:cbca:8a4b with SMTP id ffacd0b85a97d-3a074e0e1a8mr2130263f8f.6.1745591847600; 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> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: 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: h1mZFwoPaYOqessNjqdOB49B6_eI2zCIP-Z-4Y9wvq4_1745591848 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit 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 >> > > > >> > >> >