From: Steven Price <steven.price@xxxxxxx> Subject: x86: mm: avoid allocating struct mm_struct on the stack struct mm_struct is quite large (~1664 bytes) and so allocating on the stack may cause problems as the kernel stack size is small. Since ptdump_walk_pgd_level_core() was only allocating the structure so that it could modify the pgd argument we can instead introduce a pgd override in struct mm_walk and pass this down the call stack to where it is needed. Since the correct mm_struct is now being passed down, it is now also unnecessary to take the mmap_sem semaphore because ptdump_walk_pgd() will now take the semaphore on the real mm. [steven.price@xxxxxxx: restore missed arm64 changes] Link: http://lkml.kernel.org/r/20200108145710.34314-1-steven.price@xxxxxxx Link: http://lkml.kernel.org/r/20200108145710.34314-1-steven.price@xxxxxxx Signed-off-by: Steven Price <steven.price@xxxxxxx> Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx> Cc: Alexandre Ghiti <alex@xxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: David S. Miller <davem@xxxxxxxxxxxxx> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: James Hogan <jhogan@xxxxxxxxxx> Cc: James Morse <james.morse@xxxxxxx> Cc: Jerome Glisse <jglisse@xxxxxxxxxx> Cc: "Liang, Kan" <kan.liang@xxxxxxxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Paul Burton <paul.burton@xxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Zong Li <zong.li@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/arm64/mm/dump.c | 4 ++-- arch/x86/mm/debug_pagetables.c | 10 ++-------- arch/x86/mm/dump_pagetables.c | 18 +++++++----------- include/linux/pagewalk.h | 3 +++ include/linux/ptdump.h | 2 +- mm/pagewalk.c | 7 ++++++- mm/ptdump.c | 4 ++-- 7 files changed, 23 insertions(+), 25 deletions(-) --- a/arch/arm64/mm/dump.c~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/arch/arm64/mm/dump.c @@ -323,7 +323,7 @@ void ptdump_walk(struct seq_file *s, str } }; - ptdump_walk_pgd(&st.ptdump, info->mm); + ptdump_walk_pgd(&st.ptdump, info->mm, NULL); } static void ptdump_initialize(void) @@ -361,7 +361,7 @@ void ptdump_check_wx(void) } }; - ptdump_walk_pgd(&st.ptdump, &init_mm); + ptdump_walk_pgd(&st.ptdump, &init_mm, NULL); if (st.wx_pages || st.uxn_pages) pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found, %lu non-UXN pages found\n", --- a/arch/x86/mm/debug_pagetables.c~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/arch/x86/mm/debug_pagetables.c @@ -15,11 +15,8 @@ DEFINE_SHOW_ATTRIBUTE(ptdump); static int ptdump_curknl_show(struct seq_file *m, void *v) { - if (current->mm->pgd) { - down_read(¤t->mm->mmap_sem); + if (current->mm->pgd) ptdump_walk_pgd_level_debugfs(m, current->mm, false); - up_read(¤t->mm->mmap_sem); - } return 0; } @@ -28,11 +25,8 @@ DEFINE_SHOW_ATTRIBUTE(ptdump_curknl); #ifdef CONFIG_PAGE_TABLE_ISOLATION static int ptdump_curusr_show(struct seq_file *m, void *v) { - if (current->mm->pgd) { - down_read(¤t->mm->mmap_sem); + if (current->mm->pgd) ptdump_walk_pgd_level_debugfs(m, current->mm, true); - up_read(¤t->mm->mmap_sem); - } return 0; } --- a/arch/x86/mm/dump_pagetables.c~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/arch/x86/mm/dump_pagetables.c @@ -357,7 +357,8 @@ static void note_page(struct ptdump_stat } } -static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd, +static void ptdump_walk_pgd_level_core(struct seq_file *m, + struct mm_struct *mm, pgd_t *pgd, bool checkwx, bool dmesg) { const struct ptdump_range ptdump_ranges[] = { @@ -386,12 +387,7 @@ static void ptdump_walk_pgd_level_core(s .seq = m }; - struct mm_struct fake_mm = { - .pgd = pgd - }; - init_rwsem(&fake_mm.mmap_sem); - - ptdump_walk_pgd(&st.ptdump, &fake_mm); + ptdump_walk_pgd(&st.ptdump, mm, pgd); if (!checkwx) return; @@ -404,7 +400,7 @@ static void ptdump_walk_pgd_level_core(s void ptdump_walk_pgd_level(struct seq_file *m, struct mm_struct *mm) { - ptdump_walk_pgd_level_core(m, mm->pgd, false, true); + ptdump_walk_pgd_level_core(m, mm, mm->pgd, false, true); } void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm, @@ -415,7 +411,7 @@ void ptdump_walk_pgd_level_debugfs(struc if (user && boot_cpu_has(X86_FEATURE_PTI)) pgd = kernel_to_user_pgdp(pgd); #endif - ptdump_walk_pgd_level_core(m, pgd, false, false); + ptdump_walk_pgd_level_core(m, mm, pgd, false, false); } EXPORT_SYMBOL_GPL(ptdump_walk_pgd_level_debugfs); @@ -430,13 +426,13 @@ void ptdump_walk_user_pgd_level_checkwx( pr_info("x86/mm: Checking user space page tables\n"); pgd = kernel_to_user_pgdp(pgd); - ptdump_walk_pgd_level_core(NULL, pgd, true, false); + ptdump_walk_pgd_level_core(NULL, &init_mm, pgd, true, false); #endif } void ptdump_walk_pgd_level_checkwx(void) { - ptdump_walk_pgd_level_core(NULL, INIT_PGD, true, false); + ptdump_walk_pgd_level_core(NULL, &init_mm, INIT_PGD, true, false); } static int __init pt_dump_init(void) --- a/include/linux/pagewalk.h~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/include/linux/pagewalk.h @@ -74,6 +74,7 @@ enum page_walk_action { * mm_walk - walk_page_range data * @ops: operation to call during the walk * @mm: mm_struct representing the target process of page table walk + * @pgd: pointer to PGD; only valid with no_vma (otherwise set to NULL) * @vma: vma currently walked (NULL if walking outside vmas) * @action: next action to perform (see enum page_walk_action) * @no_vma: walk ignoring vmas (vma will always be NULL) @@ -84,6 +85,7 @@ enum page_walk_action { struct mm_walk { const struct mm_walk_ops *ops; struct mm_struct *mm; + pgd_t *pgd; struct vm_area_struct *vma; enum page_walk_action action; bool no_vma; @@ -95,6 +97,7 @@ int walk_page_range(struct mm_struct *mm void *private); int walk_page_range_novma(struct mm_struct *mm, unsigned long start, unsigned long end, const struct mm_walk_ops *ops, + pgd_t *pgd, void *private); int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops, void *private); --- a/include/linux/ptdump.h~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/include/linux/ptdump.h @@ -17,6 +17,6 @@ struct ptdump_state { const struct ptdump_range *range; }; -void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm); +void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd); #endif /* _LINUX_PTDUMP_H */ --- a/mm/pagewalk.c~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/mm/pagewalk.c @@ -206,7 +206,10 @@ static int walk_pgd_range(unsigned long const struct mm_walk_ops *ops = walk->ops; int err = 0; - pgd = pgd_offset(walk->mm, addr); + if (walk->pgd) + pgd = walk->pgd + pgd_index(addr); + else + pgd = pgd_offset(walk->mm, addr); do { next = pgd_addr_end(addr, end); if (pgd_none_or_clear_bad(pgd)) { @@ -436,11 +439,13 @@ int walk_page_range(struct mm_struct *mm */ int walk_page_range_novma(struct mm_struct *mm, unsigned long start, unsigned long end, const struct mm_walk_ops *ops, + pgd_t *pgd, void *private) { struct mm_walk walk = { .ops = ops, .mm = mm, + .pgd = pgd, .private = private, .no_vma = true }; --- a/mm/ptdump.c~x86-mm-avoid-allocating-struct-mm_struct-on-the-stack +++ a/mm/ptdump.c @@ -122,14 +122,14 @@ static const struct mm_walk_ops ptdump_o .pte_hole = ptdump_hole, }; -void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm) +void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd) { const struct ptdump_range *range = st->range; down_read(&mm->mmap_sem); while (range->start != range->end) { walk_page_range_novma(mm, range->start, range->end, - &ptdump_ops, st); + &ptdump_ops, pgd, st); range++; } up_read(&mm->mmap_sem); _
