From: Fares Mehanna faresx@amazon.de
[ Upstream commit 7eced90b202d63cdc1b9b11b1353adb1389830f9 ]
The reasons for PTEs in the kernel direct map to be marked invalid are not limited to kfence / debug pagealloc machinery. In particular, memfd_secret() also steals pages with set_direct_map_invalid_noflush().
When building the transitional page tables for kexec from the current kernel's page tables, those pages need to become regular writable pages, otherwise, if the relocation places kexec segments over such pages, a fault will occur during kexec, leading to host going dark during kexec.
This patch addresses the kexec issue by marking any PTE as valid if it is not none. While this fixes the kexec crash, it does not address the security concern that if processes owning secret memory are not terminated before kexec, the secret content will be mapped in the new kernel without being scrubbed.
Suggested-by: Jan H. Schönherr jschoenh@amazon.de Signed-off-by: Fares Mehanna faresx@amazon.de Link: https://lore.kernel.org/r/20240902163309.97113-1-faresx@amazon.de Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/mm/trans_pgd.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c index 5139a28130c08..0f7b484cb2ff2 100644 --- a/arch/arm64/mm/trans_pgd.c +++ b/arch/arm64/mm/trans_pgd.c @@ -42,14 +42,16 @@ static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr) * the temporary mappings we use during restore. */ __set_pte(dst_ptep, pte_mkwrite_novma(pte)); - } else if ((debug_pagealloc_enabled() || - is_kfence_address((void *)addr)) && !pte_none(pte)) { + } else if (!pte_none(pte)) { /* * debug_pagealloc will removed the PTE_VALID bit if * the page isn't in use by the resume kernel. It may have * been in use by the original kernel, in which case we need * to put it back in our copy to do the restore. * + * Other cases include kfence / vmalloc / memfd_secret which + * may call `set_direct_map_invalid_noflush()`. + * * Before marking this entry valid, check the pfn should * be mapped. */