Messages in this thread Patch in this message | | | Date | Fri, 17 Jan 2020 12:41:37 -0500 | From | Steven Rostedt <> | Subject | [PATCH RT 26/32] Revert "ARM: Initialize split page table locks for vector page" |
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4.19.94-rt39-rc1 stable review patch. If anyone has any objections, please let me know.
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ Upstream commit 247074c44d8c3e619dfde6404a52295d8d671d38 ]
I'm dropping this patch, with its original description:
|ARM: Initialize split page table locks for vector page | |Without this patch, ARM can not use SPLIT_PTLOCK_CPUS if |PREEMPT_RT_FULL=y because vectors_user_mapping() creates a |VM_ALWAYSDUMP mapping of the vector page (address 0xffff0000), but no |ptl->lock has been allocated for the page. An attempt to coredump |that page will result in a kernel NULL pointer dereference when |follow_page() attempts to lock the page. | |The call tree to the NULL pointer dereference is: | | do_notify_resume() | get_signal_to_deliver() | do_coredump() | elf_core_dump() | get_dump_page() | __get_user_pages() | follow_page() | pte_offset_map_lock() <----- a #define | ... | rt_spin_lock() | |The underlying problem is exposed by mm-shrink-the-page-frame-to-rt-size.patch.
The patch named mm-shrink-the-page-frame-to-rt-size.patch was dropped from the RT queue once the SPLIT_PTLOCK_CPUS feature (in a slightly different shape) went upstream (somewhere between v3.12 and v3.14).
I can see that the patch still allocates a lock which wasn't there before. However I can't trigger a kernel oops like described in the patch by triggering a coredump.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> --- arch/arm/kernel/process.c | 24 ------------------------ 1 file changed, 24 deletions(-)
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c index 8d3c7ce34c24..82ab015bf42b 100644 --- a/arch/arm/kernel/process.c +++ b/arch/arm/kernel/process.c @@ -324,30 +324,6 @@ unsigned long arch_randomize_brk(struct mm_struct *mm) } #ifdef CONFIG_MMU -/* - * CONFIG_SPLIT_PTLOCK_CPUS results in a page->ptl lock. If the lock is not - * initialized by pgtable_page_ctor() then a coredump of the vector page will - * fail. - */ -static int __init vectors_user_mapping_init_page(void) -{ - struct page *page; - unsigned long addr = 0xffff0000; - pgd_t *pgd; - pud_t *pud; - pmd_t *pmd; - - pgd = pgd_offset_k(addr); - pud = pud_offset(pgd, addr); - pmd = pmd_offset(pud, addr); - page = pmd_page(*(pmd)); - - pgtable_page_ctor(page); - - return 0; -} -late_initcall(vectors_user_mapping_init_page); - #ifdef CONFIG_KUSER_HELPERS /* * The vectors page is always readable from user space for the -- 2.24.1
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