80 lines
2.6 KiB
Diff
80 lines
2.6 KiB
Diff
From 2ce88b0fa9e476ef69ea181dbd71e56e59f84f38 Mon Sep 17 00:00:00 2001
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Message-Id: <2ce88b0fa9e476ef69ea181dbd71e56e59f84f38.1601675151.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Frank Rowand <frank.rowand@am.sony.com>
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Date: Sat, 1 Oct 2011 18:58:13 -0700
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Subject: [PATCH 080/333] ARM: Initialize split page table locks for vector
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page
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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Without this patch, ARM can not use SPLIT_PTLOCK_CPUS if
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PREEMPT_RT_FULL=y because vectors_user_mapping() creates a
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VM_ALWAYSDUMP mapping of the vector page (address 0xffff0000), but no
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ptl->lock has been allocated for the page. An attempt to coredump
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that page will result in a kernel NULL pointer dereference when
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follow_page() attempts to lock the page.
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The call tree to the NULL pointer dereference is:
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do_notify_resume()
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get_signal_to_deliver()
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do_coredump()
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elf_core_dump()
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get_dump_page()
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__get_user_pages()
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follow_page()
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pte_offset_map_lock() <----- a #define
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...
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rt_spin_lock()
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The underlying problem is exposed by mm-shrink-the-page-frame-to-rt-size.patch.
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Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
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Cc: Frank <Frank_Rowand@sonyusa.com>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Link: http://lkml.kernel.org/r/4E87C535.2030907@am.sony.com
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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arch/arm/kernel/process.c | 24 ++++++++++++++++++++++++
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1 file changed, 24 insertions(+)
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diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
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index 82ab015bf42b..8d3c7ce34c24 100644
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--- a/arch/arm/kernel/process.c
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+++ b/arch/arm/kernel/process.c
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@@ -324,6 +324,30 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
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}
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#ifdef CONFIG_MMU
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+/*
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+ * CONFIG_SPLIT_PTLOCK_CPUS results in a page->ptl lock. If the lock is not
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+ * initialized by pgtable_page_ctor() then a coredump of the vector page will
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+ * fail.
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+ */
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+static int __init vectors_user_mapping_init_page(void)
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+{
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+ struct page *page;
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+ unsigned long addr = 0xffff0000;
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+ pgd_t *pgd;
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+ pud_t *pud;
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+ pmd_t *pmd;
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+
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+ pgd = pgd_offset_k(addr);
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+ pud = pud_offset(pgd, addr);
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+ pmd = pmd_offset(pud, addr);
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+ page = pmd_page(*(pmd));
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+
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+ pgtable_page_ctor(page);
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+
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+ return 0;
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+}
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+late_initcall(vectors_user_mapping_init_page);
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+
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#ifdef CONFIG_KUSER_HELPERS
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/*
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* The vectors page is always readable from user space for the
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--
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2.17.1
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