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[109.64.2.78]) by smtp.gmail.com with ESMTPSA id x7sm19125928wmi.11.2020.12.13.10.36.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 13 Dec 2020 10:36:09 -0800 (PST) From: Ariel Marcovitch X-Google-Original-From: Ariel Marcovitch To: mpe@ellerman.id.au Cc: benh@kernel.crashing.org, paulus@samba.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Ariel Marcovitch Subject: [PATCH] powerpc: fix alignment bug whithin the init sections Date: Sun, 13 Dec 2020 20:35:56 +0200 Message-Id: <20201213183556.16976-1-ariel.marcovitch@gmail.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a bug that can cause early crashes in configurations with a .exit.text section smaller than a page and a .init.text section that ends in the beginning of a physical page (this is kinda random, which might explain why this wasn't really encountered before). The init sections are ordered like this: .init.text .exit.text .init.data Currently, these sections aren't page aligned. Because the init code is mapped read-only at runtime and because the .init.text section can potentially reside on the same physical page as .init.data, the beginning of .init.data might be mapped read-only along with .init.text. Then when the kernel tries to modify a variable in .init.data (like kthreadd_done, used in kernel_init()) the kernel panics. To avoid this, I made these sections page aligned. Fixes: 060ef9d89d18 ("powerpc32: PAGE_EXEC required for inittext") Signed-off-by: Ariel Marcovitch --- arch/powerpc/kernel/vmlinux.lds.S | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index 326e113d2e45..e3a7c90c03f4 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -179,6 +179,11 @@ SECTIONS #endif } :text + /* .init.text is made RO and .exit.text is not, so we must + * ensure these sections reside in separate physical pages. + */ + . = ALIGN(PAGE_SIZE); + /* .exit.text is discarded at runtime, not link time, * to deal with references from __bug_table */ @@ -186,6 +191,8 @@ SECTIONS EXIT_TEXT } + . = ALIGN(PAGE_SIZE); + .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { INIT_DATA } base-commit: 1398820fee515873379809a6415930ad0764b2f6 -- 2.17.1