From ff40839e018b82c4d756d035f34a63aa2d93be83 Mon Sep 17 00:00:00 2001 From: Anshuman Khandual Date: Fri, 20 Jun 2025 10:54:27 +0530 Subject: [PATCH] mm/ptdump: take the memory hotplug lock inside ptdump_walk_pgd() commit 59305202c67fea50378dcad0cc199dbc13a0e99a upstream. Memory hot remove unmaps and tears down various kernel page table regions as required. The ptdump code can race with concurrent modifications of the kernel page tables. When leaf entries are modified concurrently, the dump code may log stale or inconsistent information for a VA range, but this is otherwise not harmful. But when intermediate levels of kernel page table are freed, the dump code will continue to use memory that has been freed and potentially reallocated for another purpose. In such cases, the ptdump code may dereference bogus addresses, leading to a number of potential problems. To avoid the above mentioned race condition, platforms such as arm64, riscv and s390 take memory hotplug lock, while dumping kernel page table via the sysfs interface /sys/kernel/debug/kernel_page_tables. Similar race condition exists while checking for pages that might have been marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages which in turn calls ptdump_check_wx(). Instead of solving this race condition again, let's just move the memory hotplug lock inside generic ptdump_check_wx() which will benefit both the scenarios. Drop get_online_mems() and put_online_mems() combination from all existing platform ptdump code paths. Link: https://lkml.kernel.org/r/20250620052427.2092093-1-anshuman.khandual@arm.com Fixes: bbd6ec605c0f ("arm64/mm: Enable memory hot remove") Signed-off-by: Anshuman Khandual Acked-by: David Hildenbrand Reviewed-by: Dev Jain Acked-by: Alexander Gordeev [s390] Cc: Catalin Marinas Cc: Will Deacon Cc: Ryan Roberts Cc: Paul Walmsley Cc: Palmer Dabbelt Cc: Alexander Gordeev Cc: Gerald Schaefer Cc: Heiko Carstens Cc: Vasily Gorbik Cc: Christian Borntraeger Cc: Sven Schnelle Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- arch/arm64/mm/ptdump_debugfs.c | 3 --- arch/riscv/mm/ptdump.c | 3 --- arch/s390/mm/dump_pagetables.c | 2 -- mm/ptdump.c | 2 ++ 4 files changed, 2 insertions(+), 8 deletions(-) diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c index 68bf1a125502d..1e308328c0796 100644 --- a/arch/arm64/mm/ptdump_debugfs.c +++ b/arch/arm64/mm/ptdump_debugfs.c @@ -1,6 +1,5 @@ // SPDX-License-Identifier: GPL-2.0 #include -#include #include #include @@ -9,9 +8,7 @@ static int ptdump_show(struct seq_file *m, void *v) { struct ptdump_info *info = m->private; - get_online_mems(); ptdump_walk(m, info); - put_online_mems(); return 0; } DEFINE_SHOW_ATTRIBUTE(ptdump); diff --git a/arch/riscv/mm/ptdump.c b/arch/riscv/mm/ptdump.c index 9d5f657a251b3..1289cc6d3700c 100644 --- a/arch/riscv/mm/ptdump.c +++ b/arch/riscv/mm/ptdump.c @@ -6,7 +6,6 @@ #include #include #include -#include #include #include @@ -371,9 +370,7 @@ bool ptdump_check_wx(void) static int ptdump_show(struct seq_file *m, void *v) { - get_online_mems(); ptdump_walk(m, m->private); - put_online_mems(); return 0; } diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c index fa54f3bc0c8d3..70f184ca648f4 100644 --- a/arch/s390/mm/dump_pagetables.c +++ b/arch/s390/mm/dump_pagetables.c @@ -203,11 +203,9 @@ static int ptdump_show(struct seq_file *m, void *v) .marker = markers, }; - get_online_mems(); mutex_lock(&cpa_mutex); ptdump_walk_pgd(&st.ptdump, &init_mm, NULL); mutex_unlock(&cpa_mutex); - put_online_mems(); return 0; } DEFINE_SHOW_ATTRIBUTE(ptdump); diff --git a/mm/ptdump.c b/mm/ptdump.c index 106e1d66e9f9e..3e78bf33da420 100644 --- a/mm/ptdump.c +++ b/mm/ptdump.c @@ -153,6 +153,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd) { const struct ptdump_range *range = st->range; + get_online_mems(); mmap_write_lock(mm); while (range->start != range->end) { walk_page_range_novma(mm, range->start, range->end, @@ -160,6 +161,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd) range++; } mmap_write_unlock(mm); + put_online_mems(); /* Flush out the last page */ st->note_page(st, 0, -1, 0); -- 2.47.3