linux-kernel - [PATCH] x86/mm: don't free p4d table when it is folded at runtime.

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Date:   Mon, 25 Jun 2018 13:24:27 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: [PATCH] x86/mm: don't free p4d table when it is folded at runtime.

When the p4d page table layer is folded at runtime, the p4d_free()
should do nothing, the same as in <asm-generic/pgtable-nop4d.h>.

It seems this bug should cause double-free in efi_call_phys_epilog(),
but I don't know how to trigger that code path, so I can't confirm that
by testing.

Fixes: 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime")
Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
---
 arch/x86/include/asm/pgalloc.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
index ada6410fd2ec..fbd578daa66e 100644
--- a/arch/x86/include/asm/pgalloc.h
+++ b/arch/x86/include/asm/pgalloc.h
@@ -184,6 +184,9 @@ static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)
 
 static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
 {
+	if (!pgtable_l5_enabled())
+		return;
+
 	BUG_ON((unsigned long)p4d & (PAGE_SIZE-1));
 	free_page((unsigned long)p4d);
 }
-- 
2.16.4