Re: [PATCH] firmware: arm_scmi: fix double free in smc cleanup path

[Cristian Marussi <cristian.marussi@arm.com>]

On Fri, Jan 26, 2024 at 12:23:25PM +0000, Andre Przywara wrote:
> When the generic SCMI code tears down a channel, it calls the chan_free
> callback function, defined by each transport. Since multiple protocols
> might share the same transport_info member, chan_free() might want to
> clean up the same member multiple times. This will lead to a NULL
> pointer dereference at the second time:

Hi Andre,

thanks for this.

> 
> [    9.788824] scmi_protocol scmi_dev.1: Enabled polling mode TX channel - prot_id:16
> [    9.813091] arm-scmi firmware:scmi: SCMI Notifications - Core Enabled.
> [    9.814485] arm-scmi firmware:scmi: unable to communicate with SCMI
> [    9.824996] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> [    9.825586] Mem abort info:
> [    9.825863]   ESR = 0x0000000096000004
> [    9.826193]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    9.827625]   SET = 0, FnV = 0
> [    9.827927]   EA = 0, S1PTW = 0
> [    9.828232]   FSC = 0x04: level 0 translation fault
> [    9.828628] Data abort info:
> [    9.828909]   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
> [    9.829333]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> [    9.829745]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> [    9.830170] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000881ef8000
> [    9.830887] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
> [    9.831763] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
> [    9.832177] Modules linked in:
> [    9.832440] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 6.7.0-rc2-00124-g455ef3d016c9-dirty #793
> [    9.832997] Hardware name: FVP Base RevC (DT)
> [    9.833302] pstate: 61400009 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> [    9.833775] pc : smc_chan_free+0x3c/0x6c
> [    9.834089] lr : smc_chan_free+0x3c/0x6c
> [    9.834401] sp : ffff8000839bba00
> [    9.834652] x29: ffff8000839bba00 x28: 00000000ffffffa1 x27: ffff0008024aa350
> [    9.835227] x26: ffff800083305898 x25: ffff0008004d4a18 x24: ffff000800328000
> [    9.835804] x23: ffff0008024aa1b0 x22: 0000000000000000 x21: 000000007fffffff
> [    9.836375] x20: 0000000000000000 x19: ffff000802639440 x18: 0000000000000010
> [    9.836945] x17: 73203e3d20293062 x16: 3161613432303830 x15: 303066666666202c
> [    9.837522] x14: 00000000000001f4 x13: ffff000800328488 x12: 00000000ffffffea
> [    9.838094] x11: 00000000ffff7fff x10: 00000000ffff7fff x9 : ffff800082f3b430
> [    9.838667] x8 : 00000000000bffe8 x7 : c0000000ffff7fff x6 : 000000000005fff4
> [    9.839237] x5 : 00000000002bffa8 x4 : 0000000000000000 x3 : 0000000000000000
> [    9.839803] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 000000000000004a
> [    9.840368] Call trace:
> [    9.840571]  smc_chan_free+0x3c/0x6c
> [    9.840868]  idr_for_each+0x68/0xf8
> [    9.841164]  scmi_cleanup_channels.isra.0+0x2c/0x58
> [    9.841543]  scmi_probe+0x434/0x734
> [    9.841848]  platform_probe+0x68/0xd8
> [    9.842164]  really_probe+0x110/0x27c
> [    9.842464]  __driver_probe_device+0x78/0x12c
> [    9.842801]  driver_probe_device+0x3c/0x118
> [    9.843130]  __driver_attach+0x74/0x128
> [    9.843439]  bus_for_each_dev+0x78/0xe0
> [    9.843783]  driver_attach+0x24/0x30
> [    9.844121]  bus_add_driver+0xe4/0x1e8
> [    9.844466]  driver_register+0x60/0x128
> [    9.844778]  __platform_driver_register+0x28/0x34
> [    9.845149]  scmi_driver_init+0x84/0xc0
> [    9.845459]  do_one_initcall+0x78/0x33c
> [    9.845778]  kernel_init_freeable+0x2b8/0x51c
> [    9.846127]  kernel_init+0x24/0x130
> [    9.846426]  ret_from_fork+0x10/0x20
> [    9.846772] Code: f0004701 910a0021 aa1403e5 97b91c70 (b9400280)
> [    9.847172] ---[ end trace 0000000000000000 ]---
> [    9.847604] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> 
> Simply check for the struct pointer being NULL before trying to access
> its members, to avoid this situation.
> This was found when a transport doesn't really work (for instance no SMC
> service), the probe routines then tries to clean up, and triggers a crash.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Fixes: 1dc6558062da ("firmware: arm_scmi: Add smc/hvc transport")

LGTM, maybe explicitly saying in the commit message that it is an issue
of the SMC transport would be better, but I think Sudeep can easily add
such a remark without the need to post a V2.

> ---
> Hi,
> 
> reportedly Cristian has some patches in the making that solve this
> problem in a more general way, but meanwhile this is an easy backport
> candidate.

Yes, this fix is definitely needed as it is, beside any possible future
improvement in the core.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>

Thanks,
Cristian

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