RE: [PATCH v2] hv: hyperv.h: Replace one-element array with flexible-array member
From: Michael Kelley (LINUX)
Date: Wed Aug 16 2023 - 01:09:27 EST
From: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> Sent: Tuesday, August 15, 2023 9:35 PM
>
> One-element and zero-length arrays are deprecated. Replace one-element
> array in struct vmtransfer_page_packet_header with flexible-array
> member. This change fixes below warning:
>
> [ 2.593788]
> ================================================================================
> [ 2.593908] UBSAN: array-index-out-of-bounds in drivers/net/hyperv/netvsc.c:1445:41
> [ 2.593989] index 1 is out of range for type 'vmtransfer_page_range [1]'
> [ 2.594049] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.5.0-rc4-next-20230803+ #1
> [ 2.594114] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 04/20/2023
> [ 2.594121] Call Trace:
> [ 2.594126] <IRQ>
> [ 2.594133] dump_stack_lvl+0x4c/0x70
> [ 2.594154] dump_stack+0x14/0x20
> [ 2.594162] __ubsan_handle_out_of_bounds+0xa6/0xf0
> [ 2.594224] netvsc_poll+0xc01/0xc90 [hv_netvsc]
> [ 2.594258] __napi_poll+0x30/0x1e0
> [ 2.594320] net_rx_action+0x194/0x2f0
> [ 2.594333] __do_softirq+0xde/0x31e
> [ 2.594345] __irq_exit_rcu+0x6b/0x90
> [ 2.594357] irq_exit_rcu+0x12/0x20
> [ 2.594366] sysvec_hyperv_callback+0x84/0x90
> [ 2.594376] </IRQ>
> [ 2.594379] <TASK>
> [ 2.594383] asm_sysvec_hyperv_callback+0x1f/0x30
> [ 2.594394] RIP: 0010:pv_native_safe_halt+0xf/0x20
> [ 2.594452] Code: 0b 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90
> 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 05 35 3f 00 fb f4 <c3> cc cc cc cc 66 2e 0f
> 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
> [ 2.594459] RSP: 0018:ffffb841c00d3e88 EFLAGS: 00000256
> [ 2.594469] RAX: ffff9d18c326f4a0 RBX: ffff9d18c031df40 RCX: 4000000000000000
> [ 2.594475] RDX: 0000000000000001 RSI: 0000000000000082 RDI: 00000000000268dc
> [ 2.594481] RBP: ffffb841c00d3e90 R08: 00000066a171109b R09: 00000000d33d2600
> [ 2.594486] R10: 000000009a41bf00 R11: 0000000000000000 R12: 0000000000000001
> [ 2.594491] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [ 2.594501] ? ct_kernel_exit.constprop.0+0x7d/0x90
> [ 2.594513] ? default_idle+0xd/0x20
> [ 2.594523] arch_cpu_idle+0xd/0x20
> [ 2.594532] default_idle_call+0x30/0xe0
> [ 2.594542] do_idle+0x200/0x240
> [ 2.594553] ? complete+0x71/0x80
> [ 2.594613] cpu_startup_entry+0x24/0x30
> [ 2.594624] start_secondary+0x12d/0x160
> [ 2.594634] secondary_startup_64_no_verify+0x17e/0x18b
> [ 2.594649] </TASK>
> [ 2.594656]
> ================================================================================
>
> With this change the structure size is reduced by 8 bytes, below is the
> pahole output.
>
> struct vmtransfer_page_packet_header {
> struct vmpacket_descriptor d; /* 0 16 */
> u16 xfer_pageset_id; /* 16 2 */
> u8 sender_owns_set; /* 18 1 */
> u8 reserved; /* 19 1 */
> u32 range_cnt; /* 20 4 */
> struct vmtransfer_page_range ranges[]; /* 24 0 */
>
> /* size: 24, cachelines: 1, members: 6 */
> /* last cacheline: 24 bytes */
> };
>
> The validation code in the netvsc driver is affected by changing the
> struct size, but the effects have been examined and have been determined
> to be appropriate.
>
> Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> ---
> [V2]
> - Added more info in commit message regarding netvsc validation code
> affected by change of this struct.
>
> include/linux/hyperv.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 3ac3974b3c78..5c66640ea8db 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -348,7 +348,7 @@ struct vmtransfer_page_packet_header {
> u8 sender_owns_set;
> u8 reserved;
> u32 range_cnt;
> - struct vmtransfer_page_range ranges[1];
> + struct vmtransfer_page_range ranges[];
> } __packed;
>
> struct vmgpadl_packet_header {
> --
> 2.34.1
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>