From:   Rongwei Wang <rongwei.wang@linux.alibaba.com>
To:     catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com,
        james.morse@arm.com, ardb@kernel.org, tabba@google.com,
        akpm@linux-foundation.org, rppt@kernel.org,
        anshuman.khandual@arm.com
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/2] arm64: trans_pgd: fix incorrect use of pmd_populate_kernel in copy_pte()
Date:   Mon, 15 Nov 2021 04:16:49 +0800
Message-Id: <20211114201650.5542-2-rongwei.wang@linux.alibaba.com>
In-Reply-To: <20211114201650.5542-1-rongwei.wang@linux.alibaba.com>
References: <20211030183200.51295-1-rongwei.wang@linux.alibaba.com>
 <20211114201650.5542-1-rongwei.wang@linux.alibaba.com>
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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 make a simple change, just restoring init_mm
for 'pmd_populate_kernel' in 'copy_pte'.

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index d7da8ca40d2e..5275ca312360 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);
 
 	src_ptep = pte_offset_kernel(src_pmdp, start);
-- 
2.27.0