Re: [PATCH] optee: Disable shm cache when booting the crash kernel

On 2021-05-06 22:58:16, Tyler Hicks wrote:

The .shutdown hook is not called after a kernel crash when a kdump kernel is pre-loaded. A kexec into the kdump kernel takes place as quickly as possible without allowing drivers to clean up.

That means that the OP-TEE shared memory cache, which was initialized by the kernel that crashed, is still in place when the kdump kernel is booted. As the kdump kernel is shutdown, the .shutdown hook is called, which calls optee_disable_shm_cache(), and OP-TEE's OPTEE_SMC_DISABLE_SHM_CACHE API returns virtual addresses that are not mapped for the kdump kernel since the cache was set up by the previous kernel. Trying to dereference the tee_shm pointer or otherwise translate the address results in a fault that cannot be handled:

Unable to handle kernel paging request at virtual address ffff4317b9c09744 Mem abort info: ESR = 0x96000004 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000004 CM = 0, WnR = 0 swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000970b1e000 [ffff4317b9c09744] pgd=0000000000000000, p4d=0000000000000000 Internal error: Oops: 96000004 [#1] SMP Modules linked in: bnxt_en pcie_iproc_platform pcie_iproc diagbe(O) CPU: 4 PID: 1 Comm: systemd-shutdow Tainted: G O 5.10.19.8 #1 Hardware name: Redacted (DT) pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) pc : tee_shm_free (/usr/src/kernel/drivers/tee/tee_shm.c:363) lr : optee_disable_shm_cache (/usr/src/kernel/drivers/tee/optee/call.c:441) sp : ffff80001005bb70 x29: ffff80001005bb70 x28: ffff608e74648e00 x27: ffff80001005bb98 x26: dead000000000100 x25: ffff80001005bbb8 x24: aaaaaaaaaaaaaaaa x23: ffff608e74cf8818 x22: ffff608e738be600 x21: ffff80001005bbc8 x20: ffff608e738be638 x19: ffff4317b9c09700 x18: ffffffffffffffff x17: 0000000000000041 x16: ffffba61b5171764 x15: 0000000000000004 x14: 0000000000000fff x13: ffffba61b5c9dfc8 x12: 0000000000000003 x11: 0000000000000000 x10: 0000000000000000 x9 : ffffba61b5413824 x8 : 00000000ffff4317 x7 : 0000000000000000 x6 : 0000000000000000 x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 x2 : ffff4317b9c09700 x1 : 00000000ffff4317 x0 : ffff4317b9c09700 Call trace: tee_shm_free (/usr/src/kernel/drivers/tee/tee_shm.c:363) optee_disable_shm_cache (/usr/src/kernel/drivers/tee/optee/call.c:441) optee_shutdown (/usr/src/kernel/drivers/tee/optee/core.c:636) platform_drv_shutdown (/usr/src/kernel/drivers/base/platform.c:800) device_shutdown (/usr/src/kernel/include/linux/device.h:758 /usr/src/kernel/drivers/base/core.c:4078) kernel_restart (/usr/src/kernel/kernel/reboot.c:221 /usr/src/kernel/kernel/reboot.c:248) __arm64_sys_reboot (/usr/src/kernel/kernel/reboot.c:349 /usr/src/kernel/kernel/reboot.c:312 /usr/src/kernel/kernel/reboot.c:312) do_el0_svc (/usr/src/kernel/arch/arm64/kernel/syscall.c:56 /usr/src/kernel/arch/arm64/kernel/syscall.c:158 /usr/src/kernel/arch/arm64/kernel/syscall.c:197) el0_svc (/usr/src/kernel/arch/arm64/kernel/entry-common.c:368) el0_sync_handler (/usr/src/kernel/arch/arm64/kernel/entry-common.c:428) el0_sync (/usr/src/kernel/arch/arm64/kernel/entry.S:671) Code: aa0003f3 b5000060 12800003 14000002 (b9404663)

When booting the kdump kernel, drain the shared memory cache while being careful to not translate the addresses returned from OPTEE_SMC_DISABLE_SHM_CACHE. Once the invalid cache objects are drained and the cache is disabled, proceed with re-enabling the cache so that we aren't dealing with invalid addresses while shutting down the kdump kernel.

Signed-off-by: Tyler Hicks tyhicks@linux.microsoft.com

This patch fixes a crash introduced by "optee: fix tee out of memory failure seen during kexec reboot"[1]. However, I don't think that the original two patch series[2] plus this patch is the full solution to properly handling OP-TEE shared memory across kexec.

While testing this fix, I did about 10 kexec reboots and then triggered a kernel crash by writing 'c' to /proc/sysrq-trigger. The kdump kernel became unresponsive during boot while steadily streaming the following errors to the serial console:

arm-smmu 64000000.mmu: Blocked unknown Stream ID 0x2000; boot with "arm-smmu.disable_bypass=0" to allow, but this may have security implications arm-smmu 64000000.mmu: GFSR 0x00000002, GFSYNR0 0x00000002, GFSYNR1 0x00002000, GFSYNR2 0x00000000

I suspect that this is related to the problems of OP-TEE shared memory handling across kexec. My current hunch is that while we've disabled the shared memory cache with this patch, we haven't unregistered all of the addresses that the previous kernel (which crashed) had registered with OP-TEE and that perhaps OP-TEE OS is still trying to make use those addresses?

I'm still pretty early in investigating that assumption and I'm learning about OP-TEE as I go but I wanted to get this initial fix-of-the-fix out so that it was clear that the v2 of the series[2] is not complete.

[1] https://lore.kernel.org/lkml/20210225090610.242623-2-allen.lkml@gmail.com/ [2] https://lore.kernel.org/lkml/20210225090610.242623-1-allen.lkml@gmail.com/#t

drivers/tee/optee/call.c | 11 ++++++++++- drivers/tee/optee/core.c | 13 +++++++++++-- drivers/tee/optee/optee_private.h | 2 +- 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/tee/optee/call.c b/drivers/tee/optee/call.c index 6132cc8d014c..799e84bec63d 100644 --- a/drivers/tee/optee/call.c +++ b/drivers/tee/optee/call.c @@ -417,8 +417,10 @@ void optee_enable_shm_cache(struct optee *optee)

• optee_disable_shm_cache() - Disables caching of some shared memory allocation

• 	      in OP-TEE
  

• @optee: main service struct

• • @is_mapped: true if the cached shared memory addresses were mapped by this

• • kernel, are safe to dereference, and should be freed
    

  */

-void optee_disable_shm_cache(struct optee *optee) +void optee_disable_shm_cache(struct optee *optee, bool is_mapped) { struct optee_call_waiter w; @@ -437,6 +439,13 @@ void optee_disable_shm_cache(struct optee *optee) if (res.result.status == OPTEE_SMC_RETURN_OK) { struct tee_shm *shm;

• 	/*
  

• 	 * Shared memory references that were not mapped by
  

• 	 * this kernel must be ignored to prevent a crash.
  

• 	 */
  

• 	if (!is_mapped)
  

• 		continue;
  

• shm = reg_pair_to_ptr(res.result.shm_upper32,
  		      res.result.shm_lower32);
  tee_shm_free(shm);
  

diff --git a/drivers/tee/optee/core.c b/drivers/tee/optee/core.c index 69d1f698907c..9985c671bd1f 100644 --- a/drivers/tee/optee/core.c +++ b/drivers/tee/optee/core.c @@ -6,6 +6,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/arm-smccc.h> +#include <linux/crash_dump.h> #include <linux/errno.h> #include <linux/io.h> #include <linux/module.h> @@ -588,7 +589,7 @@ static int optee_remove(struct platform_device *pdev) * reference counters and also avoid wild pointers in secure world * into the old shared memory range. */

• optee_disable_shm_cache(optee);

• optee_disable_shm_cache(optee, true);

/* * The two devices have to be unregistered before we can free the @@ -618,7 +619,7 @@ static int optee_remove(struct platform_device *pdev) */ static void optee_shutdown(struct platform_device *pdev) {

• optee_disable_shm_cache(platform_get_drvdata(pdev));

• optee_disable_shm_cache(platform_get_drvdata(pdev), true);

} static int optee_probe(struct platform_device *pdev) @@ -705,6 +706,14 @@ static int optee_probe(struct platform_device *pdev) optee->memremaped_shm = memremaped_shm; optee->pool = pool;

• /*

• * The kexec into the crash kernel did not call our .shutdown hook. The
  

• * shm cache objects registered with OP-TEE are not valid for the crash
  

• * kernel.
  

• */
  

• if (is_kdump_kernel())

• optee_disable_shm_cache(optee, false);
  

Additional testing showed that only clearing the shm cache when booting the kdump kernel isn't quite enough. A kexec from an old kernel, without Allen's fix ("optee: fix OOM seen due to tee_shm_free()"), to a new kernel that contain the fix can still result in stale/invalid shm cache addresses hanging around in the secure world. When the fixed kernel is shutdown, it can still experience a crash and/or memory corruption because the secure world returns bad addresses from OPTEE_SMC_DISABLE_SHM_CACHE that are not valid for the current kernel.

In order to safely support kexec within the OP-TEE driver, I think the best option is going to always do a call to optee_disable_shm_cache() prior to calling optee_enable_shm_cache() in optee_probe().

This series is in need of a v3 with all the new knowledge/fixes after testing kexec/kdump more with OP-TEE. I'll try to get a v3 out in the coming days.

Tyler

• optee_enable_shm_cache(optee);

if (optee->sec_caps & OPTEE_SMC_SEC_CAP_DYNAMIC_SHM) diff --git a/drivers/tee/optee/optee_private.h b/drivers/tee/optee/optee_private.h index e25b216a14ef..16d8c82213e7 100644 --- a/drivers/tee/optee/optee_private.h +++ b/drivers/tee/optee/optee_private.h @@ -158,7 +158,7 @@ int optee_invoke_func(struct tee_context *ctx, struct tee_ioctl_invoke_arg *arg, int optee_cancel_req(struct tee_context *ctx, u32 cancel_id, u32 session); void optee_enable_shm_cache(struct optee *optee); -void optee_disable_shm_cache(struct optee *optee); +void optee_disable_shm_cache(struct optee *optee, bool is_mapped); int optee_shm_register(struct tee_context *ctx, struct tee_shm *shm, struct page **pages, size_t num_pages, -- 2.25.1