Re: [PATCH] arm64: mm: assign PXN permission in trans_pgd
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-11-11 16:11:22
On Thu, Nov 11, 2021 at 02:03:16PM +0800, Pingfan Liu wrote:
trans_pgd_create_copy() can hit "VM_BUG_ON(mm != &init_mm)" in the function pmd_populate_kernel().
I think that's more important to fix than the PXN. You may want to change the subject to something like "Fix VM_BUG_ON ..."
p?d_populate() helpers resort to the input parameter mm_struct to decide the attribute: UXN or PXN. And plus the fact, either hibernation or kexec runs in privilege mode. So the bug can be fixed by assigning &init_mm to the callsites of these helpers.
That's the table PXN, so it's not a big deal if we miss it.
Signed-off-by: Pingfan Liu <redacted> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: James Morse <james.morse@arm.com> Cc: Matthias Brugger <mbrugger@suse.com> To: linux-arm-kernel@lists.infradead.org
A Fixes: tag would be nice, we just need to decide which.
quoted hunk ↗ jump to hunk
--- arch/arm64/mm/trans_pgd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c index d7da8ca40d2e..7b43d179e94d 100644 --- a/arch/arm64/mm/trans_pgd.c +++ b/arch/arm64/mm/trans_pgd.c@@ -67,7 +67,7 @@ static int copy_pte(struct trans_pgd_info *info, pmd_t *dst_pmdp, dst_ptep = trans_alloc(info); if (!dst_ptep) return -ENOMEM; - pmd_populate_kernel(NULL, dst_pmdp, dst_ptep); + pmd_populate_kernel(&init_mm, dst_pmdp, dst_ptep); dst_ptep = pte_offset_kernel(dst_pmdp, start);
Commit 5de59884ac0e ("arm64: trans_pgd: pass NULL instead of init_mm to
*_populate functions") actually replaced &init_mm with NULL. Commit
59511cfd08f3 ("arm64: mm: use XN table mapping attributes for
user/kernel mappings") introduced the VM_BUG_ON.
So we either revert Pasha's trans_pgd commit (as per your patch) or we
fix Ard's commit to make it aware of a NULL mm and either skip the table
UXN altogether or treat it as init_mm.
--
Catalin
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