On Thu, Jan 16, 2020 at 11:27:58AM +0100, Libor Pechacek wrote:

In KVM guests drmem structure is only zero initialized. Trying to manipulate DLPAR parameters results in a crash in this environment.

$ echo "memory add count 1" > /sys/kernel/dlpar Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: af_packet(E) rfkill(E) nvram(E) vmx_crypto(E) gf128mul(E) e1000(E) virtio_balloon(E) rtc_generic(E) crct10dif_vpmsum(E) btrfs(E) blake2b_generic(E) libcrc32c(E) xor(E) raid6_pq(E) virtio_rng(E) virtio_blk(E) ohci_pci(E) ehci_pci(E) ohci_hcd(E) ehci_hcd(E) crc32c_vpmsum(E) usbcore(E) virtio_pci(E) virtio_ring(E) virtio(E) sg(E) dm_multipath(E) dm_mod(E) scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) scsi_mod(E) CPU: 1 PID: 4114 Comm: bash Kdump: loaded Tainted: G E 5.5.0-rc6-2-default #1 NIP: c0000000000ff294 LR: c0000000000ff248 CTR: 0000000000000000 REGS: c0000000fb9d3880 TRAP: 0300 Tainted: G E (5.5.0-rc6-2-default) MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 28242428 XER: 20000000 CFAR: c0000000009a6c10 DAR: 0000000000000010 DSISR: 40000000 IRQMASK: 0 GPR00: c0000000000ff248 c0000000fb9d3b10 c000000001682e00 0000000000000033 GPR04: c0000000ff30bf90 c0000000ff394800 0000000000005110 ffffffffffffffe8 GPR08: 0000000000000000 0000000000000000 00000000fe1c0000 0000000000000000 GPR12: 0000000000002200 c00000003fffee00 0000000000000000 000000011cbc37c0 GPR16: 000000011cb27ed0 0000000000000000 000000011cb6dd10 0000000000000000 GPR20: 000000011cb7db28 000001003ce035f0 000000011cbc7828 000000011cbc6c70 GPR24: 000001003cf01210 0000000000000000 c0000000ffade4e0 c000000002d7216b GPR28: 0000000000000001 c000000002d78560 0000000000000000 c0000000015458d0 NIP [c0000000000ff294] dlpar_memory+0x6e4/0xd00 LR [c0000000000ff248] dlpar_memory+0x698/0xd00 Call Trace: [c0000000fb9d3b10] [c0000000000ff248] dlpar_memory+0x698/0xd00 (unreliable) [c0000000fb9d3ba0] [c0000000000f5990] handle_dlpar_errorlog+0xc0/0x190 [c0000000fb9d3c10] [c0000000000f5c58] dlpar_store+0x198/0x4a0 [c0000000fb9d3cd0] [c000000000c4cb00] kobj_attr_store+0x30/0x50 [c0000000fb9d3cf0] [c0000000005a37b4] sysfs_kf_write+0x64/0x90 [c0000000fb9d3d10] [c0000000005a2c90] kernfs_fop_write+0x1b0/0x290 [c0000000fb9d3d60] [c0000000004a2bec] __vfs_write+0x3c/0x70 [c0000000fb9d3d80] [c0000000004a6560] vfs_write+0xd0/0x260 [c0000000fb9d3dd0] [c0000000004a69ac] ksys_write+0xdc/0x130 [c0000000fb9d3e20] [c00000000000b478] system_call+0x5c/0x68 Instruction dump: ebc90000 1ce70018 38e7ffe8 7cfe3a14 7fbe3840 419dff14 fb610068 7fc9f378 39000000 4800000c 60000000 4195fef4 <81490010> 39290018 38c80001 7ea93840 ---[ end trace cc2dd8152608c295 ]---

Taking closer look at the code, I can see that for_each_drmem_lmb is a macro expanding into `for (lmb = &drmem_info->lmbs[0]; lmb <= &drmem_info->lmbs[drmem_info->n_lmbs - 1]; lmb++)`. When drmem_info->lmbs is NULL, the loop would iterate through the whole address range if it weren't stopped by the NULL pointer dereference on the next line.

This patch aligns for_each_drmem_lmb and for_each_drmem_lmb_in_range macro behavior with the common C semantics, where the end marker does not belong to the scanned range, and alters get_lmb_range() semantics. As a side effect, the wraparound observed in the crash is prevented.

Fixes: 6c6ea53725b3 ("powerpc/mm: Separate ibm, dynamic-memory data from DT format") Cc: Michal Suchanek msuchanek@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Libor Pechacek lpechacek@suse.cz

Reviewed-by: Michal Suchanek msuchanek@suse.de

---

arch/powerpc/include/asm/drmem.h | 4 ++-- arch/powerpc/platforms/pseries/hotplug-memory.c | 4 ++-- 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h index 3d76e1c388c2..28c3d936fdf3 100644 --- a/arch/powerpc/include/asm/drmem.h +++ b/arch/powerpc/include/asm/drmem.h @@ -27,12 +27,12 @@ struct drmem_lmb_info { extern struct drmem_lmb_info *drmem_info; #define for_each_drmem_lmb_in_range(lmb, start, end) \

• for ((lmb) = (start); (lmb) <= (end); (lmb)++)

• for ((lmb) = (start); (lmb) < (end); (lmb)++)

#define for_each_drmem_lmb(lmb) \ for_each_drmem_lmb_in_range((lmb), \ &drmem_info->lmbs[0], \

• &drmem_info->lmbs[drmem_info->n_lmbs - 1])
  

• &drmem_info->lmbs[drmem_info->n_lmbs])
  

/*

• The of_drconf_cell_v1 struct defines the layout of the LMB data

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c index c126b94d1943..4ea6af002e27 100644 --- a/arch/powerpc/platforms/pseries/hotplug-memory.c +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c @@ -236,9 +236,9 @@ static int get_lmb_range(u32 drc_index, int n_lmbs, if (!start) return -EINVAL;

• end = &start[n_lmbs - 1];

• end = &start[n_lmbs];

• last_lmb = &drmem_info->lmbs[drmem_info->n_lmbs - 1];

• last_lmb = &drmem_info->lmbs[drmem_info->n_lmbs]; if (end > last_lmb) return -EINVAL;

2.24.1

-- Libor Pechacek SUSE Labs Remember to have fun...