Messages in this thread |  | | Date | Mon, 1 Nov 2021 10:14:22 +0800 | Subject | Re: [PATCH 1/2] arm64: trans_pgd: fix incorrect use of pmd_populate_kernel in copy_pte() | From | Rongwei Wang <> |
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On 10/31/21 8:25 PM, Ard Biesheuvel wrote: > On Sat, 30 Oct 2021 at 20:32, Rongwei Wang > <rongwei.wang@linux.alibaba.com> wrote: >> >> In commit 5de59884ac0e ("arm64: trans_pgd: pass NULL instead >> of init_mm to *_populate functions"), simply replace init_mm >> with NULL for pmd_populate_kernel. But in commit 59511cfd08f3 >> ("arm64: mm: use XN table mapping attributes for user/kernel >> mappings"), adding the check of mm context in >> pmd_populate_kernel. And these changes will cause a crash when >> executing copy_pte/trans_pgd.c, as follows: >> >> kernel BUG at arch/arm64/include/asm/pgalloc.h:79! >> Internal error: Oops - BUG: 0 [#1] SMP >> Modules linked in: rfkill(E) aes_ce_blk(E) aes_ce_cipher(E) ... >> CPU: 21 PID: 1617 Comm: a.out Kdump: loaded Tainted: ... 5.15.0-rc7-mm1+ #8 >> Hardware name: ECS, BIOS 0.0.0 02/06/2015 >> pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >> pc : trans_pgd_create_copy+0x4ac/0x4f0 >> lr : trans_pgd_create_copy+0x34c/0x4f0 >> sp : ffff80001bf2bc50 >> x29: ffff80001bf2bc50 x28: ffff0010067f1000 x27: ffff800011072000 >> x26: ffff001fffff8000 x25: ffff008000000000 x24: 0040000000000041 >> x23: 0040000000000001 x22: ffff80001bf2bd68 x21: ffff80001188ded8 >> x20: ffff800000000000 x19: ffff000000000000 x18: 0000000000000000 >> x17: 0000000000000000 x16: 0000000000000000 x15: 00000000200004c0 >> x14: ffff00003fffffff x13: ffff007fffffffff x12: ffff800010f882a8 >> x11: 0000000000face57 x10: 0000000000000001 x9 : 0000000000000000 >> x8 : ffff00100cece000 x7 : ffff001001c9f000 x6 : ffff00100ae40000 >> x5 : 0000000000000040 x4 : 0000000000000000 x3 : ffff001fffff7000 >> x2 : ffff000000200000 x1 : ffff000040000000 x0 : ffff00100cecd000 >> Call trace: >> trans_pgd_create_copy+0x4ac/0x4f0 >> machine_kexec_post_load+0x94/0x3bc >> do_kexec_load+0x11c/0x2e0 >> __arm64_sys_kexec_load+0xa8/0xf4 >> invoke_syscall+0x50/0x120 >> el0_svc_common.constprop.0+0x58/0x190 >> do_el0_svc+0x2c/0x90 >> el0_svc+0x28/0xe0 >> el0t_64_sync_handler+0xb0/0xb4 >> el0t_64_sync+0x180/0x184 >> Code: f90000c0 d5033a9f d5033fdf 17ffff7b (d4210000) >> ---[ end trace cc5461ffe1a085db ]--- >> Kernel panic - not syncing: Oops - BUG: Fatal exception >> >> This bug can be reproduced by a user case: >> >> void execute_kexec_load(void) >> { >> syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul); >> syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul); >> syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul); >> >> *(uint64_t*)0x200004c0 = 0; >> *(uint64_t*)0x200004c8 = 0; >> *(uint64_t*)0x200004d0 = 0; >> *(uint64_t*)0x200004d8 = 0; >> syscall(__NR_kexec_load, 0ul, 1ul, 0x200004c0ul, 0ul); >> } >> >> And this patch just make some simple changes, and including >> replace pmd_populate_kernel with pmd_populate. >> >> Fixes: 59511cfd08f3 ("arm64: mm: use XN table mapping attributes for user/kernel mappings") >> Reported-by: Abaci <abaci@linux.alibaba.com> >> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> >> --- >> arch/arm64/mm/trans_pgd.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c >> index d7da8ca40d2e..3f1fc6cb9c9d 100644 >> --- a/arch/arm64/mm/trans_pgd.c >> +++ b/arch/arm64/mm/trans_pgd.c >> @@ -62,12 +62,13 @@ static int copy_pte(struct trans_pgd_info *info, pmd_t *dst_pmdp, >> { >> pte_t *src_ptep; >> pte_t *dst_ptep; >> + struct page *page; >> unsigned long addr = start; >> >> - dst_ptep = trans_alloc(info); >> - if (!dst_ptep) >> + page = virt_to_page(trans_alloc(info)); >> + if (!page) >> return -ENOMEM; >> - pmd_populate_kernel(NULL, dst_pmdp, dst_ptep); >> + pmd_populate(NULL, dst_pmdp, page); > > Are you sure this truly fixes the underlying issue rather than the symptom? > Hi Ard
I just found bug line on 'VM_BUG_ON(mm != &init_mm)' shown below, seems a obvious incorrect use of 'pmd_populate_kernel' in copy_pte. It seems these changes were introduced in this year.
static inline void pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmdp, pte_t *ptep) { VM_BUG_ON(mm != &init_mm); __pmd_populate(pmdp, __pa(ptep), PMD_TYPE_TABLE | PMD_TABLE_UXN); }
And I had run some testcases, not triggered this bug any more. If I missing something, please remind me! And I will check it again.
Thanks!
> pmd_populate() will create a table entry with the PXN attribute set, > which means nothing below it will be executable by the kernel, > regardless of the executable permissions at the PTE level. > > >> dst_ptep = pte_offset_kernel(dst_pmdp, start); >> >> src_ptep = pte_offset_kernel(src_pmdp, start); >> -- >> 2.27.0 >>
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