[PATCH v2] x86/mm: fix kern_addr_valid to cope with existing but not present entries

From: Mike Rapoport
Date: Thu Aug 19 2021 - 09:27:32 EST

From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

Jiri Olsa reported a fault when running:

# cat /proc/kallsyms | grep ksys_read
ffffffff8136d580 T ksys_read
# objdump -d --start-address=0xffffffff8136d580 --stop-address=0xffffffff8136d590 /proc/kcore

/proc/kcore: file format elf64-x86-64

Segmentation fault

krava33 login: [ 68.330612] general protection fault, probably for non-canonical address 0xf887ffcbff000: 0000 [#1] SMP PTI
[ 68.333118] CPU: 12 PID: 1079 Comm: objdump Not tainted 5.14.0-rc5qemu+ #508
[ 68.334922] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-4.fc34 04/01/2014
[ 68.336945] RIP: 0010:kern_addr_valid+0x150/0x300
[ 68.338082] Code: 1f 40 00 48 8b 0d e8 12 61 01 48 85 f6 0f 85 ca 00 00 00 48 81 e1 00 f0 ff ff 48 21 c1 48 b8 00 00 00 00 80 88 ff ff 48 01 ca <48> 8b 3c 02 48 f7 c7 9f ff ff ff 0f 84 d8 fe ff ff 48 89 f8 0f 1f
[ 68.342220] RSP: 0018:ffffc90000bcbc38 EFLAGS: 00010206
[ 68.343428] RAX: ffff888000000000 RBX: 0000000000001000 RCX: 000ffffffcbff000
[ 68.345029] RDX: 000ffffffcbff000 RSI: 0000000000000000 RDI: 800ffffffcbff062
[ 68.346599] RBP: ffffc90000bcbea8 R08: 0000000000001000 R09: 0000000000000000
[ 68.349000] R10: 0000000000000000 R11: 0000000000001000 R12: 00007fcc0fd80010
[ 68.350804] R13: ffffffff83400000 R14: 0000000000400000 R15: ffffffff843d23e0
[ 68.352609] FS: 00007fcc111fcc80(0000) GS:ffff888275e00000(0000) knlGS:0000000000000000
[ 68.354638] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 68.356104] CR2: 00007fcc0fd80000 CR3: 000000011226e004 CR4: 0000000000770ee0
[ 68.357896] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 68.359694] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 68.361597] PKRU: 55555554
[ 68.362460] Call Trace:
[ 68.363252] read_kcore+0x57f/0x920
[ 68.364289] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.365630] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.366955] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.368277] ? trace_hardirqs_on+0x1b/0xd0
[ 68.369462] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.370793] ? lock_acquire+0x195/0x2f0
[ 68.371920] ? lock_acquire+0x195/0x2f0
[ 68.373035] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.374364] ? lock_acquire+0x195/0x2f0
[ 68.375498] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.376831] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.379883] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.381268] ? lock_release+0x22b/0x3e0
[ 68.382458] ? _raw_spin_unlock+0x1f/0x30
[ 68.383685] ? __handle_mm_fault+0xcfc/0x15f0
[ 68.384994] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.386389] ? lock_acquire+0x195/0x2f0
[ 68.387573] ? rcu_read_lock_sched_held+0x12/0x80
[ 68.388969] ? lock_release+0x22b/0x3e0
[ 68.390145] proc_reg_read+0x55/0xa0
[ 68.391257] ? vfs_read+0x78/0x1b0
[ 68.392336] vfs_read+0xa7/0x1b0
[ 68.393328] ksys_read+0x68/0xe0
[ 68.394308] do_syscall_64+0x3b/0x90
[ 68.395391] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 68.396804] RIP: 0033:0x7fcc11cf92e2
[ 68.397824] Code: c0 e9 b2 fe ff ff 50 48 8d 3d ea 2e 0a 00 e8 95 e9 01 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24
[ 68.402420] RSP: 002b:00007ffd6e0f8da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 68.404357] RAX: ffffffffffffffda RBX: 0000565439305b20 RCX: 00007fcc11cf92e2
[ 68.406061] RDX: 0000000000800000 RSI: 00007fcc0f980010 RDI: 0000000000000003
[ 68.407747] RBP: 00007fcc11dcd300 R08: 0000000000000003 R09: 00007fcc0d980010
[ 68.410937] R10: 0000000003826000 R11: 0000000000000246 R12: 00007fcc0f980010
[ 68.412624] R13: 0000000000000d68 R14: 00007fcc11dcc700 R15: 0000000000800000
[ 68.414322] Modules linked in: intel_rapl_msr intel_rapl_common nfit kvm_intel kvm irqbypass rapl iTCO_wdt iTCO_vendor_support i2c_i801 i2c_smbus lpc_ich drm drm_panel_orientation_quirks zram xfs crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel
[ 68.419591] ---[ end trace e2c30f827226966b ]---
[ 68.420969] RIP: 0010:kern_addr_valid+0x150/0x300
[ 68.422308] Code: 1f 40 00 48 8b 0d e8 12 61 01 48 85 f6 0f 85 ca 00 00 00 48 81 e1 00 f0 ff ff 48 21 c1 48 b8 00 00 00 00 80 88 ff ff 48 01 ca <48> 8b 3c 02 48 f7 c7 9f ff ff ff 0f 84 d8 fe ff ff 48 89 f8 0f 1f
[ 68.426826] RSP: 0018:ffffc90000bcbc38 EFLAGS: 00010206
[ 68.428150] RAX: ffff888000000000 RBX: 0000000000001000 RCX: 000ffffffcbff000
[ 68.429813] RDX: 000ffffffcbff000 RSI: 0000000000000000 RDI: 800ffffffcbff062
[ 68.431465] RBP: ffffc90000bcbea8 R08: 0000000000001000 R09: 0000000000000000
[ 68.433115] R10: 0000000000000000 R11: 0000000000001000 R12: 00007fcc0fd80010
[ 68.434768] R13: ffffffff83400000 R14: 0000000000400000 R15: ffffffff843d23e0
[ 68.436423] FS: 00007fcc111fcc80(0000) GS:ffff888275e00000(0000) knlGS:0000000000000000
[ 68.438354] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 68.442077] CR2: 00007fcc0fd80000 CR3: 000000011226e004 CR4: 0000000000770ee0
[ 68.443727] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 68.445370] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 68.447010] PKRU: 55555554

The fault happens because kern_addr_valid() dereferences existent but not
present PMD in the high kernel mappings.

Such PMDs are created when free_kernel_image_pages() frees regions larger
than 2Mb. In this case a part of the freed memory is mapped with PMDs and
the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will
mark the PMD as not present rather than wipe it completely.

Make kern_addr_valid() to check whether higher level page table entries are
present before trying to dereference them to fix this issue and to avoid
similar issues in the future.

Reported-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.4+
---

v2:
* drop pXd_none() checks and leave only pXd_present(), per David

v1: https://lore.kernel.org/lkml/20210817135854.25407-1-rppt@xxxxxxxxxx

arch/x86/mm/init_64.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index ddeaba947eb3..879886c6cc53 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1433,18 +1433,18 @@ int kern_addr_valid(unsigned long addr)
return 0;

p4d = p4d_offset(pgd, addr);
- if (p4d_none(*p4d))
+ if (!p4d_present(*p4d))
return 0;

pud = pud_offset(p4d, addr);
- if (pud_none(*pud))
+ if (!pud_present(*pud))
return 0;

if (pud_large(*pud))
return pfn_valid(pud_pfn(*pud));

pmd = pmd_offset(pud, addr);
- if (pmd_none(*pmd))
+ if (!pmd_present(*pmd))
return 0;

if (pmd_large(*pmd))
--
2.28.0