From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 9E94115AD9C for ; Fri, 29 Nov 2024 10:56:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732877793; cv=none; b=SZegPbMy9/T6dNbr3AsygjI/7A5uaErczjd2wjEKOYrYiztwVWAVVZtguJnS1eqHGe94km+TGZcEpSmzHkKKiLjbuvxMQniLSSFuomVHuiHnOtbYz/fkJPF64w40tBnUwUD27barjzCtmm/Ffmi19+SCXSigXJV++b2AOfQ6KFA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732877793; c=relaxed/simple; bh=Wvxe7aofJUvEmbjRHsju7bN6rhkOG6gSuLk4Mp+zkUo=; h=Date:To:From:Subject:Message-Id; b=P949LFCAWvCUsGfxdRuje1jwF2wSgm7KjBEkoQI9EH1ruhaSAhUbtQLTEGOCwfTc+biaWz8AuEgjYHew1qkKzxWLhMHEWnLSC7NIgkmuE7/Vld16fH9hR6nkvJ2wjzFf+dnRdk3ms0Rc+pi7W5lLZ0VZDwPf5+V6yulXkIKilrk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=yPM8ga1D; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="yPM8ga1D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F3CF0C4CECF; Fri, 29 Nov 2024 10:56:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1732877793; bh=Wvxe7aofJUvEmbjRHsju7bN6rhkOG6gSuLk4Mp+zkUo=; h=Date:To:From:Subject:From; b=yPM8ga1Dpmi284WnzMGkWGRjCWo9dyOnI8R/GyZxs3WN6zCfWqQwXcvXP69e1qK3s p8HqCSOOOPG2C9z0APf1i1O6Alo7tsD1kZD1iXC4GKWt9m4hoEfMoE4Sf9aNXhDPye bCqJz/nJZZZXWlISDBOa5SVberWpWxYaa6DJ7A+A= Date: Fri, 29 Nov 2024 02:56:32 -0800 To: mm-commits@vger.kernel.org,kees@kernel.org,jinb.park7@gmail.com,ptesarik@suse.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-rodata_test-use-read_once-to-read-const-variable.patch added to mm-unstable branch Message-Id: <20241129105632.F3CF0C4CECF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/rodata_test: use READ_ONCE() to read const variable has been added to the -mm mm-unstable branch. Its filename is mm-rodata_test-use-read_once-to-read-const-variable.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rodata_test-use-read_once-to-read-const-variable.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Petr Tesarik Subject: mm/rodata_test: use READ_ONCE() to read const variable Date: Tue, 19 Nov 2024 12:37:38 +0100 Patch series "Fix mm/rodata_test", v2. Make sure that the test actually reads the read-only memory location. Verify that the variable contains the expected value rather than any non-zero value. This patch (of 2): The C compiler may optimize away the memory read of a const variable if its value is known at compile time. In particular, GCC14 with -O2 generates no code at all for test 1, and it generates the following x86_64 instructions for test 3: cmpl $195, 4(%rsp) je .L14 That is, it replaces the read of rodata_test_data with an immediate value and compares it to the value of the local variable "zero". Use READ_ONCE() to undo any such compiler optimizations and enforce a memory read. Link: https://lkml.kernel.org/r/cover.1732016064.git.ptesarik@suse.com Link: https://lkml.kernel.org/r/2a66dee010151b25cb143efb39091ef7530aa00a.1732016064.git.ptesarik@suse.com Fixes: 2959a5f726f6 ("mm: add arch-independent testcases for RODATA") Signed-off-by: Petr Tesarik Reviewed-by: Kees Cook Cc: Jinbum Park Signed-off-by: Andrew Morton --- mm/rodata_test.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/rodata_test.c~mm-rodata_test-use-read_once-to-read-const-variable +++ a/mm/rodata_test.c @@ -20,7 +20,7 @@ void rodata_test(void) /* test 1: read the value */ /* If this test fails, some previous testrun has clobbered the state */ - if (!rodata_test_data) { + if (!READ_ONCE(rodata_test_data)) { pr_err("test 1 fails (start data)\n"); return; } @@ -33,7 +33,7 @@ void rodata_test(void) } /* test 3: check the value hasn't changed */ - if (rodata_test_data == zero) { + if (READ_ONCE(rodata_test_data) == zero) { pr_err("test data was changed\n"); return; } _ Patches currently in -mm which might be from ptesarik@suse.com are mm-rodata_test-use-read_once-to-read-const-variable.patch mm-rodata_test-verify-test-data-is-unchanged-rather-than-non-zero.patch