Re: [PATCH v2] iommu/qcom: fix NULL pointer dereference during probe deferral

From: Robin Murphy
Date: Mon Jan 06 2020 - 08:27:03 EST

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On 04/01/2020 12:20 am, Brian Masney wrote:

When attempting to load the qcom-iommu driver, and an -EPROBE_DEFER
error occurs, the following attempted NULL pointer deference occurs:

Unable to handle kernel NULL pointer dereference at virtual address 00000014
pgd = (ptrval)
[00000014] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc2-next-20191220-00010-gfb6b8e8bced6-dirty #3
Hardware name: Generic DT based system
PC is at qcom_iommu_domain_free (include/linux/pm_runtime.h:226
drivers/iommu/qcom_iommu.c:358)
LR is at release_iommu_mapping (arch/arm/mm/dma-mapping.c:2141)
pc : lr : psr: 60000013
sp : ee89dc48 ip : 00000000 fp : c13a6684
r10: c13a661c r9 : 00000000 r8 : c13a1240
r7 : fffffdfb r6 : 00000000 r5 : edc32f00 r4 : edc32f1c
r3 : 00000000 r2 : 00000001 r1 : 00000004 r0 : edc32f1c
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 10c5787d Table: 0020406a DAC: 00000051
Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
Stack: (0xee89dc48 to 0xee89e000)
dc40: edc3d010 edc37020 00000000 c0316af8 edc3d010 edc37000
dc60: 00000000 c0319684 c14341ac edc3d010 00000000 c083bd88 edc3d010 c13a1240
dc80: c083c2e8 c13a6684 c13a661c c13a6508 c13a661c c083c134 c13a1240 ee89dcec
dca0: edc3d010 00000000 ee89dcec c083c2e8 c13a6684 c13a661c c13a6508 c13a661c
dcc0: c13a6684 c083a31c c13a6684 ee82a86c edc327b8 c1304e48 edc3d010 00000001
dce0: edc3d054 c083bc08 ee82a880 edc3d010 00000001 c1304e48 edc3d010 edc3d010
dd00: c13a69e8 c083b010 edc3d010 00000000 eea1fc10 c0837aac 00000200 00000000
dd20: 00000000 00000000 00000000 c1304e48 00000000 edc3d000 eea1fc10 00000000
dd40: 00000000 eeff42f4 00000000 00000001 00000000 c09e96e0 eeff42a4 00000000
dd60: 00000000 00000000 eea1fc10 c09e98bc 00000001 eea1fc10 00000000 eea1fc10
dd80: edc32c00 c1391580 eea1fc10 00000001 eea1fc10 c0850f90 c2706dec c14368c0
dda0: 60000013 c1304e48 00000106 eeff42a4 eeff3fa0 00000000 00000000 eea1fc10
ddc0: 00000001 c1248900 00000106 c09e9bd0 00000001 c0c2ee64 eea1fc00 eea1fc10
dde0: eea1fc10 00000000 c13a5b70 00000000 c1248900 c081496c c1023d84 00000000
de00: eeff3fa0 c2706e48 c2706e48 c1304e48 00000001 00000000 eea1fc10 c13a5b70
de20: 00000000 c13a5b70 00000000 c1248900 00000106 c083dfb8 c14341ac eea1fc10
de40: 00000000 c083be58 eea1fc10 c13a5b70 c13a5b70 c13a69e8 c12003ec c123a854
de60: c1248900 c083c134 c1248900 c09e6f3c c0d8d514 eea1fc10 00000000 c13a5b70
de80: c13a69e8 c12003ec c123a854 c1248900 00000106 c083c3e0 00000000 c13a5b70
dea0: eea1fc10 c083c440 00000000 c13a5b70 c083c3e8 c083a23c 00000106 ee82a858
dec0: eea052b4 c1304e48 c13a5b70 edc32b80 00000000 c083b270 c1043084 c121d1d8
dee0: ffffe000 c13a5b70 c121d1d8 ffffe000 00000000 c083cfcc c13ece60 c121d1d8
df00: ffffe000 c0302f90 00000106 c034407c 00000000 c10e3a00 c1044dd0 c12003ec
df20: 00000000 00000006 00000006 c0fbecac c0fada88 c0fada3c 00000000 efffcbf8
df40: efffcc0d c1304e48 00000000 00000006 c13f9500 c1304e48 c123a830 00000007
df60: c13f9500 c13f9500 c123a834 c1200f64 00000006 00000006 00000000 c12003ec
df80: c0c28194 00000000 c0c28194 00000000 00000000 00000000 00000000 00000000
dfa0: 00000000 c0c2819c 00000000 c03010e8 00000000 00000000 00000000 00000000
dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
dfe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
(qcom_iommu_domain_free) from release_iommu_mapping
(arch/arm/mm/dma-mapping.c:2141)
(release_iommu_mapping) from arch_teardown_dma_ops
(include/linux/dma-mapping.h:271 arch/arm/mm/dma-mapping.c:2335)
(arch_teardown_dma_ops) from really_probe (drivers/base/dd.c:607)
(really_probe) from driver_probe_device (drivers/base/dd.c:721)
(driver_probe_device) from bus_for_each_drv (drivers/base/bus.c:431)
(bus_for_each_drv) from __device_attach (drivers/base/dd.c:896)
(__device_attach) from bus_probe_device (drivers/base/bus.c:491)
(bus_probe_device) from device_add (drivers/base/core.c:2488)
(device_add) from of_platform_device_create_pdata
(drivers/of/platform.c:189)
(of_platform_device_create_pdata) from of_platform_bus_create
(drivers/of/platform.c:393 drivers/of/platform.c:346)
(of_platform_bus_create) from of_platform_populate
(drivers/of/platform.c:486)
(of_platform_populate) from msm_pdev_probe
(drivers/gpu/drm/msm/msm_drv.c:1197 drivers/gpu/drm/msm/msm_drv.c:1281)
(msm_pdev_probe) from platform_drv_probe (drivers/base/platform.c:726)
(platform_drv_probe) from really_probe (drivers/base/dd.c:553)
(really_probe) from driver_probe_device (drivers/base/dd.c:721)
(driver_probe_device) from device_driver_attach (drivers/base/dd.c:995)
(device_driver_attach) from __driver_attach (drivers/base/dd.c:1074)
(__driver_attach) from bus_for_each_dev (drivers/base/bus.c:304)
(bus_for_each_dev) from bus_add_driver (drivers/base/bus.c:623)
(bus_add_driver) from driver_register (drivers/base/driver.c:172)
(driver_register) from do_one_initcall (include/linux/compiler.h:232
include/linux/jump_label.h:254 include/linux/jump_label.h:264
include/trace/events/initcall.h:48 init/main.c:941)
(do_one_initcall) from kernel_init_freeable (init/main.c:1013
init/main.c:1022 init/main.c:1039 init/main.c:1231)
(kernel_init_freeable) from kernel_init (init/main.c:1127)
(kernel_init) from ret_from_fork (arch/arm/kernel/entry-common.S:156)

qcom_iommu_domain_free() has a WARN_ON() that checks to see if the value
of iommu is NULL and returns early, so iommu->dev will always be NULL.
qcom_iommu_detach_dev() is called prior to freeing the IOMMU domain and
is what sets the iommu member to NULL.

Let's fix this by adding the 'struct dev' pointer to the
qcom_iommu_domain struct.

Actually, it looks like the qcom_domain->iommu logic is fundamentally broken anyway - this sequence of calls is perfectly valid, but AFAICS will make qcom-iommu go horribly wrong:

dom = iommu_domain_alloc(...);
iommu_attach_device(dom, dev1);
iommu_attach_device(dom, dev2);
iommu_detach_device(dom, dev2);
// dev1 still attached but dom->iommu now NULL

Furthermore, even this should technically be valid:

dom = iommu_domain_alloc(...);
iommu_attach_device(dom, dev);
iommu_map(dom, addr, ...);
iommu_detach_device(dom, dev);
iommu_unmap(dom, addr, ...); // oops, dereferences NULL again

Does something like the diff below work?

Robin.

----->8-----
diff --git a/drivers/iommu/qcom_iommu.c b/drivers/iommu/qcom_iommu.c
index c31e7bc4ccbe..af6ee4bf1712 100644
--- a/drivers/iommu/qcom_iommu.c
+++ b/drivers/iommu/qcom_iommu.c
@@ -345,21 +345,20 @@ static void qcom_iommu_domain_free(struct iommu_domain *domain)
{
struct qcom_iommu_domain *qcom_domain = to_qcom_iommu_domain(domain);

- if (WARN_ON(qcom_domain->iommu)) /* forgot to detach? */
- return;
-
iommu_put_dma_cookie(domain);

- /* NOTE: unmap can be called after client device is powered off,
- * for example, with GPUs or anything involving dma-buf. So we
- * cannot rely on the device_link. Make sure the IOMMU is on to
- * avoid unclocked accesses in the TLB inv path:
- */
- pm_runtime_get_sync(qcom_domain->iommu->dev);
+ if (qcom_domain->iommu) {
+ /* NOTE: unmap can be called after client device is powered off,
+ * for example, with GPUs or anything involving dma-buf. So we
+ * cannot rely on the device_link. Make sure the IOMMU is on to
+ * avoid unclocked accesses in the TLB inv path:
+ */
+ pm_runtime_get_sync(qcom_domain->iommu->dev);

- free_io_pgtable_ops(qcom_domain->pgtbl_ops);
+ free_io_pgtable_ops(qcom_domain->pgtbl_ops);

- pm_runtime_put_sync(qcom_domain->iommu->dev);
+ pm_runtime_put_sync(qcom_domain->iommu->dev);
+ }

kfree(qcom_domain);
}
@@ -405,7 +404,7 @@ static void qcom_iommu_detach_dev(struct iommu_domain *domain, struct device *de
struct qcom_iommu_domain *qcom_domain = to_qcom_iommu_domain(domain);
unsigned i;

- if (!qcom_domain->iommu)
+ if (WARN_ON(!qcom_domain->iommu))
return;

pm_runtime_get_sync(qcom_iommu->dev);
@@ -418,8 +417,6 @@ static void qcom_iommu_detach_dev(struct iommu_domain *domain, struct device *de
ctx->domain = NULL;
}
pm_runtime_put_sync(qcom_iommu->dev);
-
- qcom_domain->iommu = NULL;
}

static int qcom_iommu_map(struct iommu_domain *domain, unsigned long iova,

Next message: Alain Volmat: "[PATCH 1/6] ARM: dts: stm32: add i2c4 sleep pinctrl on stm32mp15xx-dkx"
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In reply to: Brian Masney: "[PATCH v2] iommu/qcom: fix NULL pointer dereference during probe deferral"
Next in thread: Brian Masney: "Re: [PATCH v2] iommu/qcom: fix NULL pointer dereference during probe deferral"
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