linux-kernel - [PATCH 5.15 053/179] arm64: mm: Fix VM_BUG_ON(mm != &init_mm) for trans

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Message-Id: <20211129181720.719044173@linuxfoundation.org>
Date:   Mon, 29 Nov 2021 19:17:27 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pingfan Liu <kernelfans@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        James Morse <james.morse@....com>,
        Matthias Brugger <mbrugger@...e.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH 5.15 053/179] arm64: mm: Fix VM_BUG_ON(mm != &init_mm) for trans_pgd

From: Pingfan Liu <kernelfans@...il.com>

commit d3eb70ead6474ec16f976fcacf10a7a890a95bd3 upstream.

trans_pgd_create_copy() can hit "VM_BUG_ON(mm != &init_mm)" in the
function pmd_populate_kernel().

This is the combined consequence of commit 5de59884ac0e ("arm64:
trans_pgd: pass NULL instead of init_mm to *_populate functions"), which
replaced &init_mm with NULL and commit 59511cfd08f3 ("arm64: mm: use XN
table mapping attributes for user/kernel mappings"), which introduced
the VM_BUG_ON.

Since the former sounds reasonable, it is better to work on the later.
>>From the perspective of trans_pgd, two groups of functions are
considered in the later one:

  pmd_populate_kernel()
    mm == NULL should be fixed, else it hits VM_BUG_ON()
  p?d_populate()
    mm == NULL means PXN, that is OK, since trans_pgd only copies a
    linear map, no execution will happen on the map.

So it is good enough to just relax VM_BUG_ON() to disregard mm == NULL

Fixes: 59511cfd08f3 ("arm64: mm: use XN table mapping attributes for user/kernel mappings")
Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: <stable@...r.kernel.org> # 5.13.x
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: James Morse <james.morse@....com>
Cc: Matthias Brugger <mbrugger@...e.com>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@...een.com>
Link: https://lore.kernel.org/r/20211112052214.9086-1-kernelfans@gmail.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/include/asm/pgalloc.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/include/asm/pgalloc.h
+++ b/arch/arm64/include/asm/pgalloc.h
@@ -76,7 +76,7 @@ static inline void __pmd_populate(pmd_t
 static inline void
 pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmdp, pte_t *ptep)
 {
-	VM_BUG_ON(mm != &init_mm);
+	VM_BUG_ON(mm && mm != &init_mm);
 	__pmd_populate(pmdp, __pa(ptep), PMD_TYPE_TABLE | PMD_TABLE_UXN);
 }