[PATCH] crypto: caam - use the same jr for rng init/exit

[Horia Geanta <horia.geanta@nxp.com>]

On 9/4/2019 5:35 AM, Andrey Smirnov wrote:
> In order to allow caam_jr_enqueue() to lock underlying JR's
> device (via device_lock(), see commit that follows) we need to make
> sure that no code calls caam_jr_enqueue() as a part of caam_jr_probe()
> to avoid a deadlock. Unfortunately, current implementation of caamrng
> code does exactly that in caam_init_buf().
> 
> Another big problem with original caamrng initialization is a
> circular reference in the form of:
> 
>  1. caam_rng_init() aquires JR via caam_jr_alloc(). Freed only by
>     caam_rng_exit()
> 
>  2. caam_rng_exit() is only called by unregister_algs() once last JR
>     is shut down
> 
>  3. caam_jr_remove() won't call unregister_algs() for last JR
>     until tfm_count reaches zero, which can only happen via
>     unregister_algs() -> caam_rng_exit() call chain.
> 
> To avoid all of that, convert caamrng code to a platform device driver
> and extend caam_probe() to create corresponding platform device.
> 
> Additionally, this change also allows us to remove any access to
> struct caam_drv_private in caamrng.c as well as simplify resource
> ownership/deallocation via devres.
> 
I would avoid adding platform devices that don't have
corresponding DT nodes.

There's some generic advice here:
https://www.kernel.org/doc/html/latest/driver-api/driver-model/platform.html#legacy-drivers-device-probing

and there's also previous experience in caam driver:
6b175685b4a1 crypto: caam/qi - don't allocate an extra platform device

The issue in caamrng is actually that caam/jr driver (jr.c) tries to call
caam_rng_exit() on the last available jr device.
Instead, caam_rng_exit() must be called on the same jr device that
was used during caam_rng_init().

Otherwise, by the time:

void caam_rng_exit(void)
{
        if (!init_done)
                return;

        caam_jr_free(rng_ctx->jrdev);
	hwrng_unregister(&caam_rng);
[...]

is executed, rng_ctx->jrdev might have been removed.

This will cause an oops in caam_jr_free().
caam_cleanup() - .cleanup hwrng callback that is called when doing
hwrng_unregister() - also needs to be executed on that jr device.

The problem can be easily reproduced as follows.

If caamrng was initialized on jr0:
[...]
caam_jr 2101000.jr0: registering rng-caam
[...]

then by manually unbinding jr0 first, then jr1 (using i.MX6SX):
# echo -n "2101000.jr0" > /sys/bus/platform/drivers/caam_jr/
# echo -n "2102000.jr1" > /sys/bus/platform/drivers/caam_jr/

Unable to handle kernel NULL pointer dereference at virtual address 00000040
pgd = 572e14e7
[00000040] *pgd=be2e8831
Internal error: Oops: 17 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 629 Comm: sh Not tainted 5.3.0-rc1-00299-g8e2a2738e5d3-dirty #8
Hardware name: Freescale i.MX6 SoloX (Device Tree)
PC is at caam_jr_free+0xc/0x24
LR is at caam_rng_exit+0x20/0x3c
pc : [<c08aef20>]    lr : [<c08bab1c>]    psr: 200f0013
sp : e9669e68  ip : 00001488  fp : 00000000
r10: 00000000  r9 : e9669f80  r8 : e9284010
r7 : e872d410  r6 : e872d410  r5 : e872d400  r4 : c1aa7cd8
r3 : 00000000  r2 : 00000040  r1 : 00000000  r0 : e872d010
Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: a969004a  DAC: 00000051
Process sh (pid: 629, stack limit = 0xfc1b6e94)
Stack: (0xe9669e68 to 0xe966a000)
9e60:                   e865c940 c08af7dc e872d410 e872d410 c13a9cec c06b223c
9e80: c06b2218 e872d410 e81a9410 c06b08dc c13806f0 0000000b c13a9cec c06aeaf8
9ea0: 0000000b 00000000 0000000b e9284000 e91189c0 c0318c3c 00000000 00000000
9ec0: e95ddbd0 e8843500 c1308b08 c6614c9f e8843500 00438340 e9668000 00000004
9ee0: 00000000 c0285e00 00000001 00000000 00000000 c0288a44 00000000 00000000
9f00: c1308b28 00000000 00000001 c130911c 00000001 c13e81d1 c0288a44 00000000
9f20: e8ed9800 c019df00 e8ed9a7c c028ac08 00000001 00000000 c0288a44 c6614c9f
9f40: c1308b08 0000000b 00438340 e9669f80 e8843500 00438340 e9668000 c028899c
9f60: e95ddbc0 c6614c9f e8843500 e8843500 c1308b08 0000000b 00438340 c0288bfc
9f80: 00000000 00000000 00000000 c6614c9f 0000000b 00438340 b6ef1da0 00000004
9fa0: c01011c4 c0101000 0000000b 00438340 00000001 00438340 0000000b 00000000
9fc0: 0000000b 00438340 b6ef1da0 00000004 00438340 0000000b 00000000 00000000
9fe0: 0000006c bea7f908 b6e19e58 b6e7325c 600f0010 00000001 00000000 00000000
[<c08aef20>] (caam_jr_free) from [<c08bab1c>] (caam_rng_exit+0x20/0x3c)
[<c08bab1c>] (caam_rng_exit) from [<c08af7dc>] (caam_jr_remove+0x38/0xc0)
[<c08af7dc>] (caam_jr_remove) from [<c06b223c>] (platform_drv_remove+0x24/0x3c)
[<c06b223c>] (platform_drv_remove) from [<c06b08dc>] (device_release_driver_internal+0xdc/0x1a0)
[<c06b08dc>] (device_release_driver_internal) from [<c06aeaf8>] (unbind_store+0x5c/0xcc)
[<c06aeaf8>] (unbind_store) from [<c0318c3c>] (kernfs_fop_write+0xfc/0x1e0)
[<c0318c3c>] (kernfs_fop_write) from [<c0285e00>] (__vfs_write+0x2c/0x1d0)
[<c0285e00>] (__vfs_write) from [<c028899c>] (vfs_write+0xa0/0x180)
[<c028899c>] (vfs_write) from [<c0288bfc>] (ksys_write+0x5c/0xdc)
[<c0288bfc>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xe9669fa8 to 0xe9669ff0)
9fa0:                   0000000b 00438340 00000001 00438340 0000000b 00000000
9fc0: 0000000b 00438340 b6ef1da0 00000004 00438340 0000000b 00000000 00000000
9fe0: 0000006c bea7f908 b6e19e58 b6e7325c
Code: eaffff49 e5903040 e2832040 f5d2f000 (e1921f9f)

Thus, I'd say the following fix is needed:

-- >8 --

When caam_rng_exit() executes, the jr device that was used
during caam_rng_init() must be available.

This means that current scheme - where caam_rng_exit() is called
when last jr device is removed - is incorrect.
Instead, caam_rng_exit() has to run when the jr acquired
during caam_rng_init() is removed.

Fixes: 1b46c90c8e00 ("crypto: caam - convert top level drivers to libraries")
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>

diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.c
index e8baacaabe07..ec40178fa688 100644
--- a/drivers/crypto/caam/caamrng.c
+++ b/drivers/crypto/caam/caamrng.c
@@ -300,9 +300,9 @@ static struct hwrng caam_rng = {
        .read           = caam_read,
 };

-void caam_rng_exit(void)
+void caam_rng_exit(struct device *jrdev)
 {
-       if (!init_done)
+       if (!init_done || jrdev != rng_ctx->jrdev)
                return;

        caam_jr_free(rng_ctx->jrdev);
diff --git a/drivers/crypto/caam/intern.h b/drivers/crypto/caam/intern.h
index 731b06becd9c..4795530203ad 100644
--- a/drivers/crypto/caam/intern.h
+++ b/drivers/crypto/caam/intern.h
@@ -165,7 +165,7 @@ static inline void caam_pkc_exit(void)
 #ifdef CONFIG_CRYPTO_DEV_FSL_CAAM_RNG_API

 int caam_rng_init(struct device *dev);
-void caam_rng_exit(void);
+void caam_rng_exit(struct device *jrdev);

 #else

@@ -174,7 +174,7 @@ static inline int caam_rng_init(struct device *dev)
        return 0;
 }

-static inline void caam_rng_exit(void)
+static inline void caam_rng_exit(struct device *jrdev)
 {
 }

diff --git a/drivers/crypto/caam/jr.c b/drivers/crypto/caam/jr.c
index d11956bc358f..61aea11773a6 100644
--- a/drivers/crypto/caam/jr.c
+++ b/drivers/crypto/caam/jr.c
@@ -53,7 +53,6 @@ static void unregister_algs(void)

        caam_qi_algapi_exit();

-       caam_rng_exit();
        caam_pkc_exit();
        caam_algapi_hash_exit();
        caam_algapi_exit();
@@ -126,6 +125,8 @@ static int caam_jr_remove(struct platform_device *pdev)
        jrdev = &pdev->dev;
        jrpriv = dev_get_drvdata(jrdev);

+       caam_rng_exit(jrdev);
+
        /*
         * Return EBUSY if job ring already allocated.
         */