Re: [PATCH] ata: ahci: Match EM_MAX_SLOTS with SATA_PMP_MAX_PORTS

[Damien Le Moal]

On 10/11/22 11:46, Kai-Heng Feng wrote:
> UBSAN complains about array-index-out-of-bounds:
> [ 1.980703] kernel: UBSAN: array-index-out-of-bounds in /build/linux-9H675w/linux-5.15.0/drivers/ata/libahci.c:968:41
> [ 1.980709] kernel: index 15 is out of range for type 'ahci_em_priv [8]'
> [ 1.980713] kernel: CPU: 0 PID: 209 Comm: scsi_eh_8 Not tainted 5.15.0-25-generic #25-Ubuntu
> [ 1.980716] kernel: Hardware name: System manufacturer System Product Name/P5Q3, BIOS 1102 06/11/2010
> [ 1.980718] kernel: Call Trace:
> [ 1.980721] kernel: <TASK>
> [ 1.980723] kernel: show_stack+0x52/0x58
> [ 1.980729] kernel: dump_stack_lvl+0x4a/0x5f
> [ 1.980734] kernel: dump_stack+0x10/0x12
> [ 1.980736] kernel: ubsan_epilogue+0x9/0x45
> [ 1.980739] kernel: __ubsan_handle_out_of_bounds.cold+0x44/0x49
> [ 1.980742] kernel: ahci_qc_issue+0x166/0x170 [libahci]
> [ 1.980748] kernel: ata_qc_issue+0x135/0x240
> [ 1.980752] kernel: ata_exec_internal_sg+0x2c4/0x580
> [ 1.980754] kernel: ? vprintk_default+0x1d/0x20
> [ 1.980759] kernel: ata_exec_internal+0x67/0xa0
> [ 1.980762] kernel: sata_pmp_read+0x8d/0xc0
> [ 1.980765] kernel: sata_pmp_read_gscr+0x3c/0x90
> [ 1.980768] kernel: sata_pmp_attach+0x8b/0x310
> [ 1.980771] kernel: ata_eh_revalidate_and_attach+0x28c/0x4b0
> [ 1.980775] kernel: ata_eh_recover+0x6b6/0xb30
> [ 1.980778] kernel: ? ahci_do_hardreset+0x180/0x180 [libahci]
> [ 1.980783] kernel: ? ahci_stop_engine+0xb0/0xb0 [libahci]
> [ 1.980787] kernel: ? ahci_do_softreset+0x290/0x290 [libahci]
> [ 1.980792] kernel: ? trace_event_raw_event_ata_eh_link_autopsy_qc+0xe0/0xe0
> [ 1.980795] kernel: sata_pmp_eh_recover.isra.0+0x214/0x560
> [ 1.980799] kernel: sata_pmp_error_handler+0x23/0x40
> [ 1.980802] kernel: ahci_error_handler+0x43/0x80 [libahci]
> [ 1.980806] kernel: ata_scsi_port_error_handler+0x2b1/0x600
> [ 1.980810] kernel: ata_scsi_error+0x9c/0xd0
> [ 1.980813] kernel: scsi_error_handler+0xa1/0x180
> [ 1.980817] kernel: ? scsi_unjam_host+0x1c0/0x1c0
> [ 1.980820] kernel: kthread+0x12a/0x150
> [ 1.980823] kernel: ? set_kthread_struct+0x50/0x50
> [ 1.980826] kernel: ret_from_fork+0x22/0x30
> [ 1.980831] kernel: </TASK>
> 
> This happens because sata_pmp_init_links() initialize link->pmp up to
> SATA_PMP_MAX_PORTS while em_priv is declared as 8 elements array.
> 
> I can't find the maximum Enclosure Management ports specified in AHCI
> spec v1.3.1, but "12.2.1 LED message type" states that "Port Multiplier
> Information" can utilize 4 bits, which implies it can support up to 16
> ports. Hence, use SATA_PMP_MAX_PORTS as EM_MAX_SLOTS to resolve the
> issue.

Yes, makes sense: em_priv declaration does say so:

	/* enclosure management info per PM slot */
	struct ahci_em_priv	em_priv[EM_MAX_SLOTS];

So if it is per pm slot and we can have at most SATA_PMP_MAX_PORTS, then
indeed EM_MAX_SLOTS should be equal to that. I wonder why a different
macro is used, but I have not dig into git log history to find out :)

> BugLink: https://bugs.launchpad.net/bugs/1970074

Ideally, this would need a Fixes tag too I. EM_MAX_SLOTS was set to 8 from
the start:

18f7ba4c2f4b ("libata/ahci: enclosure management support")

but the code has changed a lot after that.

Adding "Cc: stable@xxxxxxxxxxxxxxx" should suffice here since your fix
should apply to all stable versions (please check !).

> Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> ---
>  drivers/ata/ahci.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
> index da7ee8bec165a..7add8e79912b1 100644
> --- a/drivers/ata/ahci.h
> +++ b/drivers/ata/ahci.h
> @@ -257,7 +257,7 @@ enum {
>  	PCS_7				= 0x94, /* 7+ port PCS (Denverton) */
>  
>  	/* em constants */
> -	EM_MAX_SLOTS			= 8,
> +	EM_MAX_SLOTS			= SATA_PMP_MAX_PORTS,
>  	EM_MAX_RETRY			= 5,
>  
>  	/* em_ctl bits */

-- 
Damien Le Moal
Western Digital Research