Messages in this thread |  | | From | Ard Biesheuvel <> | Date | Sun, 31 Oct 2021 13:25:41 +0100 | Subject | Re: [PATCH 1/2] arm64: trans_pgd: fix incorrect use of pmd_populate_kernel in copy_pte() |
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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?
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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