Re: [PATCH] PCI/ASPM: fix UAF by removing cached downstream

Bjorn Helgaas
2023-05-01T02:11:01Z

On Sat, Apr 29, 2023 at 09:26:04PM +0800, Ding Hui wrote:
> If the function 0 of a multifunction device is removed, an freed
> downstream pointer will be left in struct pcie_link_state, and then
> when pcie_config_aspm_link() be invoked from any path, we will get a
> KASAN use-after-free report.

Thanks for finding this problem, debugging it, and the patch!

In this case we're doing a "software remove" and the other functions
are still present, right? It's kind of annoying that there's only one
link, but all the functions of a multifunction device have a Link
Control register, and the spec "recommends" that software program the
same ASPM control value for all the functions.

The hardware of course doesn't know anything about this software
remove; all the functions are still physically present and powered up.

That makes me think that if software ignores the "removed" function
and continues to operate ASPM on the N-1 remaining functions, we're
outside the spec recommendations because the ASPM configuration is no
longer the same across all the functions.

So my inclination would be disable ASPM completely when any function
of a multi-function device is removed. What are your thoughts on
this?

> Reproducer:
>
> [root@host ~]# cat repro.sh
> #!/bin/bash
> DEV_F0="0000:03:00.0"
> echo 1 > /sys/bus/pci/devices/$DEV_F0/remove
> echo powersave > /sys/module/pcie_aspm/parameters/policy
>
> Result:
>
> [ 177.433490] ==================================================================
> [ 177.433814] BUG: KASAN: slab-use-after-free in pcie_config_aspm_link+0x42d/0x500
> [ 177.434114] Read of size 4 at addr ffff8881070c80a0 by task repro.sh/2056
>
> [ 177.434747] CPU: 3 PID: 2056 Comm: repro.sh Not tainted 6.3.0+ #15
> [ 177.435062] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
> [ 177.435379] Call Trace:
> [ 177.435741] <TASK>
> [ 177.436058] dump_stack_lvl+0x33/0x50
> [ 177.436379] print_address_description.constprop.0+0x27/0x310
> [ 177.436733] print_report+0x3e/0x70
> [ 177.437067] ? pcie_config_aspm_link+0x42d/0x500
> [ 177.437398] kasan_report+0xae/0xe0
> [ 177.437753] ? pcie_config_aspm_link+0x42d/0x500
> [ 177.438115] pcie_config_aspm_link+0x42d/0x500
> [ 177.438447] pcie_aspm_set_policy+0x8e/0x1a0
> [ 177.438862] param_attr_store+0x162/0x2c0
> [ 177.439217] ? __pfx_sysfs_kf_write+0x10/0x10
> [ 177.439571] module_attr_store+0x3e/0x80
> [ 177.439898] kernfs_fop_write_iter+0x2d5/0x460
> [ 177.440218] vfs_write+0x72e/0xae0
> [ 177.440552] ? __pfx_vfs_write+0x10/0x10
> [ 177.440866] ? __count_memcg_events+0xea/0x1d0
> [ 177.441173] ksys_write+0xed/0x1c0
> [ 177.441519] ? __pfx_ksys_write+0x10/0x10
> [ 177.441874] do_syscall_64+0x38/0x90
> [ 177.442202] entry_SYSCALL_64_after_hwframe+0x72/0xdc
> [ 177.442547] RIP: 0033:0x7f0829a622c7
> [ 177.442922] Code: 0e 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
> [ 177.443721] RSP: 002b:00007ffc6bb2d128 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> [ 177.444151] RAX: ffffffffffffffda RBX: 000000000000000a RCX: 00007f0829a622c7
> [ 177.444572] RDX: 000000000000000a RSI: 000055b8e6b168f0 RDI: 0000000000000001
> [ 177.445049] RBP: 000055b8e6b168f0 R08: 00007f0829b12000 R09: 00007f0829b12080
> [ 177.445490] R10: 00007f0829b11f80 R11: 0000000000000246 R12: 000000000000000a
> [ 177.445984] R13: 00007f0829b535a0 R14: 000000000000000a R15: 00007f0829b53780
> [ 177.446443] </TASK>
>
> [ 177.447402] Allocated by task 1:
> [ 177.447902] kasan_save_stack+0x1e/0x40
> [ 177.448444] kasan_set_track+0x21/0x30
> [ 177.448946] __kasan_kmalloc+0x7b/0x90
> [ 177.449447] pci_alloc_dev+0x44/0x260
> [ 177.449950] pci_scan_single_device+0x132/0x280
> [ 177.450467] pci_scan_slot+0x193/0x510
> [ 177.450986] pci_scan_child_bus_extend+0x61/0x5d0
> [ 177.451528] pci_scan_bridge_extend+0xc4c/0x10c0
> [ 177.452021] pci_scan_child_bus_extend+0x332/0x5d0
> [ 177.452539] acpi_pci_root_create+0x4ec/0x700
> [ 177.453015] pci_acpi_scan_root+0x3ad/0x4e0
> [ 177.453495] acpi_pci_root_add+0x3f2/0x910
> [ 177.453973] acpi_bus_attach+0x38b/0x890
> [ 177.454415] device_for_each_child+0xd8/0x150
> [ 177.454896] acpi_dev_for_each_child+0x77/0xa0
> [ 177.455328] acpi_bus_attach+0x19f/0x890
> [ 177.455785] device_for_each_child+0xd8/0x150
> [ 177.456189] acpi_dev_for_each_child+0x77/0xa0
> [ 177.456626] acpi_bus_attach+0x19f/0x890
> [ 177.457077] acpi_bus_scan+0x98/0x160
> [ 177.457481] acpi_scan_init+0x1e3/0x3f0
> [ 177.457905] acpi_init+0xff/0x2c0
> [ 177.458300] do_one_initcall+0x87/0x300
> [ 177.458694] do_initcalls+0x127/0x260
> [ 177.459113] kernel_init_freeable+0x811/0xc80
> [ 177.459517] kernel_init+0x1b/0x1e0
> [ 177.459915] ret_from_fork+0x29/0x50
>
> [ 177.460724] Freed by task 2011:
> [ 177.461119] kasan_save_stack+0x1e/0x40
> [ 177.461556] kasan_set_track+0x21/0x30
> [ 177.461939] kasan_save_free_info+0x2a/0x50
> [ 177.462320] __kasan_slab_free+0x106/0x190
> [ 177.462737] __kmem_cache_free+0x133/0x270
> [ 177.463115] device_release+0x98/0x210
> [ 177.463492] kobject_cleanup+0x101/0x360
> [ 177.463952] pci_stop_and_remove_bus_device_locked+0xdb/0x110
> [ 177.464341] remove_store+0xcf/0xe0
> [ 177.464746] kernfs_fop_write_iter+0x2d5/0x460
> [ 177.465112] vfs_write+0x72e/0xae0
> [ 177.465493] ksys_write+0xed/0x1c0
> [ 177.465834] do_syscall_64+0x38/0x90
> [ 177.466174] entry_SYSCALL_64_after_hwframe+0x72/0xdc

We don't need ALL this detail. Most of this, including the
timestamps, register dump, and most of the backtrace, is not relevant.

> This patch is based on original RFC by Bolarinwa O. Saheed in 2021 [1],
> which using pci_function_0() to obtain child instead of cached
> downstream pointer in struct pcie_link_state.
>
> In addition, I added the condition about child to avoid dereference
> null pointer, in case the device is removed without rescan back.
>
> [1] https://lore.kernel.org/lkml/20211106175503.27178-5-refactormyself@gmail.com/
>
> --------
>
> The commit log of original patch:
>
> Information on the downstream component is cached in
> struct pcie_link_state.downstream it obtained within
> alloc_pcie_link_state() by calling pci_function_0()
>
> - remove *downstream* from the struct pcie_link_state.
> - replaces references to pcie_link_state.downstream with
> a call to pci_function_0(pdev->subordinate).
>
> Originally-by: Bolarinwa O. Saheed <refactormyself@gmail.com>
> Fixes: b5a0a9b59c81 ("PCI/ASPM: Read and set up L1 substate capabilities")
> Debugged-by: Zongquan Qin <qinzongquan@sangfor.com.cn>
> Signed-off-by: Ding Hui <dinghui@sangfor.com.cn>
> ---
> drivers/pci/pcie/aspm.c | 31 +++++++++++++++++++++++--------
> 1 file changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 66d7514ca111..bca3f52009fe 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -44,7 +44,6 @@
>
> struct pcie_link_state {
> struct pci_dev *pdev; /* Upstream component of the Link */
> - struct pci_dev *downstream; /* Downstream component, function 0 */
> struct pcie_link_state *root; /* pointer to the root port link */
> struct pcie_link_state *parent; /* pointer to the parent Link state */
> struct list_head sibling; /* node in link_list */
> @@ -474,7 +473,8 @@ static void pci_clear_and_set_dword(struct pci_dev *pdev, int pos,
> static void aspm_calc_l1ss_info(struct pcie_link_state *link,
> u32 parent_l1ss_cap, u32 child_l1ss_cap)
> {
> - struct pci_dev *child = link->downstream, *parent = link->pdev;
> + struct pci_dev *parent = link->pdev;
> + struct pci_dev *child = pci_function_0(link->pdev->subordinate);
> u32 val1, val2, scale1, scale2;
> u32 t_common_mode, t_power_on, l1_2_threshold, scale, value;
> u32 ctl1 = 0, ctl2 = 0;
> @@ -484,6 +484,9 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
> if (!(link->aspm_support & ASPM_STATE_L1_2_MASK))
> return;
>
> + if (!child)
> + return;
> +
> /* Choose the greater of the two Port Common_Mode_Restore_Times */
> val1 = (parent_l1ss_cap & PCI_L1SS_CAP_CM_RESTORE_TIME) >> 8;
> val2 = (child_l1ss_cap & PCI_L1SS_CAP_CM_RESTORE_TIME) >> 8;
> @@ -565,11 +568,12 @@ static void aspm_calc_l1ss_info(struct pcie_link_state *link,
>
> static void aspm_l1ss_init(struct pcie_link_state *link)
> {
> - struct pci_dev *child = link->downstream, *parent = link->pdev;
> + struct pci_dev *parent = link->pdev;
> + struct pci_dev *child = pci_function_0(link->pdev->subordinate);
> u32 parent_l1ss_cap, child_l1ss_cap;
> u32 parent_l1ss_ctl1 = 0, child_l1ss_ctl1 = 0;
>
> - if (!parent->l1ss || !child->l1ss)
> + if (!parent->l1ss || !child || !child->l1ss)
> return;
>
> /* Setup L1 substate */
> @@ -622,7 +626,8 @@ static void aspm_l1ss_init(struct pcie_link_state *link)
>
> static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
> {
> - struct pci_dev *child = link->downstream, *parent = link->pdev;
> + struct pci_dev *parent = link->pdev;
> + struct pci_dev *child = pci_function_0(link->pdev->subordinate);
> u32 parent_lnkcap, child_lnkcap;
> u16 parent_lnkctl, child_lnkctl;
> struct pci_bus *linkbus = parent->subordinate;
> @@ -634,6 +639,9 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
> return;
> }
>
> + if (!child)
> + return;
> +
> /*
> * If ASPM not supported, don't mess with the clocks and link,
> * bail out now.
> @@ -701,7 +709,11 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
> static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
> {
> u32 val, enable_req;
> - struct pci_dev *child = link->downstream, *parent = link->pdev;
> + struct pci_dev *parent = link->pdev;
> + struct pci_dev *child = pci_function_0(link->pdev->subordinate);
> +
> + if (!child)
> + return;
>
> enable_req = (link->aspm_enabled ^ state) & state;
>
> @@ -760,9 +772,13 @@ static void pcie_config_aspm_dev(struct pci_dev *pdev, u32 val)
> static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)
> {
> u32 upstream = 0, dwstream = 0;
> - struct pci_dev *child = link->downstream, *parent = link->pdev;
> + struct pci_dev *parent = link->pdev;
> + struct pci_dev *child = pci_function_0(link->pdev->subordinate);
> struct pci_bus *linkbus = parent->subordinate;
>
> + if (!child)
> + return;
> +
> /* Enable only the states that were not explicitly disabled */
> state &= (link->aspm_capable & ~link->aspm_disable);
>
> @@ -867,7 +883,6 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
>
> INIT_LIST_HEAD(&link->sibling);
> link->pdev = pdev;
> - link->downstream = pci_function_0(pdev->subordinate);
>
> /*
> * Root Ports and PCI/PCI-X to PCIe Bridges are roots of PCIe
> --
> 2.17.1
>