6.6-stable review patch. If anyone has any objections, please let me know.
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From: Donet Tom donettom@linux.ibm.com
[ Upstream commit 9cf7e13fecbab0894f6986fc6986ab2eba8de52e ]
A vmemmap altmap is a device-provided region used to provide backing storage for struct pages. For each namespace, the altmap should belong to that same namespace. If the namespaces are created unaligned, there is a chance that the section vmemmap start address could also be unaligned. If the section vmemmap start address is unaligned, the altmap page allocated from the current namespace might be used by the previous namespace also. During the free operation, since the altmap is shared between two namespaces, the previous namespace may detect that the page does not belong to its altmap and incorrectly assume that the page is a normal page. It then attempts to free the normal page, which leads to a kernel crash.
Kernel attempted to read user page (18) - exploit attempt? (uid: 0) BUG: Kernel NULL pointer dereference on read at 0x00000018 Faulting instruction address: 0xc000000000530c7c Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries CPU: 32 PID: 2104 Comm: ndctl Kdump: loaded Tainted: G W NIP: c000000000530c7c LR: c000000000530e00 CTR: 0000000000007ffe REGS: c000000015e57040 TRAP: 0300 Tainted: G W MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 84482404 CFAR: c000000000530dfc DAR: 0000000000000018 DSISR: 40000000 IRQMASK: 0 GPR00: c000000000530e00 c000000015e572e0 c000000002c5cb00 c00c000101008040 GPR04: 0000000000000000 0000000000000007 0000000000000001 000000000000001f GPR08: 0000000000000005 0000000000000000 0000000000000018 0000000000002000 GPR12: c0000000001d2fb0 c0000060de6b0080 0000000000000000 c0000060dbf90020 GPR16: c00c000101008000 0000000000000001 0000000000000000 c000000125b20f00 GPR20: 0000000000000001 0000000000000000 ffffffffffffffff c00c000101007fff GPR24: 0000000000000001 0000000000000000 0000000000000000 0000000000000000 GPR28: 0000000004040201 0000000000000001 0000000000000000 c00c000101008040 NIP [c000000000530c7c] get_pfnblock_flags_mask+0x7c/0xd0 LR [c000000000530e00] free_unref_page_prepare+0x130/0x4f0 Call Trace: free_unref_page+0x50/0x1e0 free_reserved_page+0x40/0x68 free_vmemmap_pages+0x98/0xe0 remove_pte_table+0x164/0x1e8 remove_pmd_table+0x204/0x2c8 remove_pud_table+0x1c4/0x288 remove_pagetable+0x1c8/0x310 vmemmap_free+0x24/0x50 section_deactivate+0x28c/0x2a0 __remove_pages+0x84/0x110 arch_remove_memory+0x38/0x60 memunmap_pages+0x18c/0x3d0 devm_action_release+0x30/0x50 release_nodes+0x68/0x140 devres_release_group+0x100/0x190 dax_pmem_compat_release+0x44/0x80 [dax_pmem_compat] device_for_each_child+0x8c/0x100 [dax_pmem_compat_remove+0x2c/0x50 [dax_pmem_compat] nvdimm_bus_remove+0x78/0x140 [libnvdimm] device_remove+0x70/0xd0
Another issue is that if there is no altmap, a PMD-sized vmemmap page will be allocated from RAM, regardless of the alignment of the section start address. If the section start address is not aligned to the PMD size, a VM_BUG_ON will be triggered when setting the PMD-sized page to page table.
In this patch, we are aligning the section vmemmap start address to PAGE_SIZE. After alignment, the start address will not be part of the current namespace, and a normal page will be allocated for the vmemmap mapping of the current section. For the remaining sections, altmaps will be allocated. During the free operation, the normal page will be correctly freed.
In the same way, a PMD_SIZE vmemmap page will be allocated only if the section start address is PMD_SIZE-aligned; otherwise, it will fall back to a PAGE-sized vmemmap allocation.
Without this patch ================== NS1 start NS2 start _________________________________________________________ | NS1 | NS2 | --------------------------------------------------------- | Altmap| Altmap | .....|Altmap| Altmap | ........... | NS1 | NS1 | | NS2 | NS2 |
In the above scenario, NS1 and NS2 are two namespaces. The vmemmap for NS1 comes from Altmap NS1, which belongs to NS1, and the vmemmap for NS2 comes from Altmap NS2, which belongs to NS2.
The vmemmap start for NS2 is not aligned, so Altmap NS2 is shared by both NS1 and NS2. During the free operation in NS1, Altmap NS2 is not part of NS1's altmap, causing it to attempt to free an invalid page.
With this patch =============== NS1 start NS2 start _________________________________________________________ | NS1 | NS2 | --------------------------------------------------------- | Altmap| Altmap | .....| Normal | Altmap | Altmap |....... | NS1 | NS1 | | Page | NS2 | NS2 |
If the vmemmap start for NS2 is not aligned then we are allocating a normal page. NS1 and NS2 vmemmap will be freed correctly.
Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function") Co-developed-by: Ritesh Harjani (IBM) ritesh.list@gmail.com Signed-off-by: Ritesh Harjani (IBM) ritesh.list@gmail.com Signed-off-by: Donet Tom donettom@linux.ibm.com Signed-off-by: Madhavan Srinivasan maddy@linux.ibm.com Link: https://patch.msgid.link/8f98ec2b442977c618f7256cec88eb17dde3f2b9.1741609795... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/mm/book3s64/radix_pgtable.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c index c6a4ac766b2bf..28460e3340808 100644 --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -1056,6 +1056,19 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in pmd_t *pmd; pte_t *pte;
+ /* + * Make sure we align the start vmemmap addr so that we calculate + * the correct start_pfn in altmap boundary check to decided whether + * we should use altmap or RAM based backing memory allocation. Also + * the address need to be aligned for set_pte operation. + + * If the start addr is already PMD_SIZE aligned we will try to use + * a pmd mapping. We don't want to be too aggressive here beacause + * that will cause more allocations in RAM. So only if the namespace + * vmemmap start addr is PMD_SIZE aligned we will use PMD mapping. + */ + + start = ALIGN_DOWN(start, PAGE_SIZE); for (addr = start; addr < end; addr = next) { next = pmd_addr_end(addr, end);
@@ -1081,8 +1094,8 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in * in altmap block allocation failures, in which case * we fallback to RAM for vmemmap allocation. */ - if (altmap && (!IS_ALIGNED(addr, PMD_SIZE) || - altmap_cross_boundary(altmap, addr, PMD_SIZE))) { + if (!IS_ALIGNED(addr, PMD_SIZE) || (altmap && + altmap_cross_boundary(altmap, addr, PMD_SIZE))) { /* * make sure we don't create altmap mappings * covering things outside the device.