Date:   Thu, 18 Aug 2022 13:08:59 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     linux-kernel@...r.kernel.org, op-tee@...ts.trustedfirmware.org
Cc:     Sumit Garg <sumit.garg@...aro.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        stable@...r.kernel.org, Nimish Mishra <neelam.nimish@...il.com>,
        Anirban Chakraborty <ch.anirban00727@...il.com>,
        Debdeep Mukhopadhyay <debdeep.mukhopadhyay@...il.com>,
        Jerome Forissier <jerome.forissier@...aro.org>
Subject: [PATCH v2] tee: add overflow check in register_shm_helper()

With special lengths supplied by user space, register_shm_helper() has
an integer overflow when calculating the number of pages covered by a
supplied user space memory region. This causes
internal_get_user_pages_fast() a helper function of
pin_user_pages_fast() to do a NULL pointer dereference.

[   14.141620] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
[   14.142556] Mem abort info:
[   14.142829]   ESR = 0x0000000096000044
[   14.143237]   EC = 0x25: DABT (current EL), IL = 32 bits
[   14.143742]   SET = 0, FnV = 0
[   14.144052]   EA = 0, S1PTW = 0
[   14.144348]   FSC = 0x04: level 0 translation fault
[   14.144767] Data abort info:
[   14.145053]   ISV = 0, ISS = 0x00000044
[   14.145394]   CM = 0, WnR = 1
[   14.145766] user pgtable: 4k pages, 48-bit VAs, pgdp=000000004278e000
[   14.146279] [0000000000000010] pgd=0000000000000000, p4d=0000000000000000
[   14.147435] Internal error: Oops: 96000044 [#1] PREEMPT SMP
[   14.148026] Modules linked in:
[   14.148595] CPU: 1 PID: 173 Comm: optee_example_a Not tainted 5.19.0 #11
[   14.149204] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
[   14.149832] pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   14.150481] pc : internal_get_user_pages_fast+0x474/0xa80
[   14.151640] lr : internal_get_user_pages_fast+0x404/0xa80
[   14.152408] sp : ffff80000a88bb30
[   14.152711] x29: ffff80000a88bb30 x28: 0000fffff836d000 x27: 0000fffff836e000
[   14.153580] x26: fffffc0000000000 x25: fffffc0000f4a1c0 x24: ffff00000289fb70
[   14.154634] x23: ffff000002702e08 x22: 0000000000040001 x21: ffff8000097eec60
[   14.155378] x20: 0000000000f4a1c0 x19: 00e800007d287f43 x18: 0000000000000000
[   14.156215] x17: 0000000000000000 x16: 0000000000000000 x15: 0000fffff836cfb0
[   14.157068] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
[   14.157747] x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
[   14.158576] x8 : ffff00000276ec80 x7 : 0000000000000000 x6 : 000000000000003f
[   14.159243] x5 : 0000000000000000 x4 : ffff000041ec4eac x3 : ffff000002774cb8
[   14.159977] x2 : 0000000000000004 x1 : 0000000000000010 x0 : 0000000000000000
[   14.160883] Call trace:
[   14.161166]  internal_get_user_pages_fast+0x474/0xa80
[   14.161763]  pin_user_pages_fast+0x24/0x4c
[   14.162227]  register_shm_helper+0x194/0x330
[   14.162734]  tee_shm_register_user_buf+0x78/0x120
[   14.163290]  tee_ioctl+0xd0/0x11a0
[   14.163739]  __arm64_sys_ioctl+0xa8/0xec
[   14.164227]  invoke_syscall+0x48/0x114
[   14.164653]  el0_svc_common.constprop.0+0x44/0xec
[   14.165130]  do_el0_svc+0x2c/0xc0
[   14.165498]  el0_svc+0x2c/0x84
[   14.165847]  el0t_64_sync_handler+0x1ac/0x1b0
[   14.166258]  el0t_64_sync+0x18c/0x190
[   14.166878] Code: 91002318 11000401 b900f7e1 f9403be1 (f820d839)
[   14.167666] ---[ end trace 0000000000000000 ]---

Fix this by adding an overflow check when calculating the end of the
memory range. Also add an explicit call to access_ok() in
tee_shm_register_user_buf() to catch an invalid user space address
early.

Fixes: 033ddf12bcf5 ("tee: add register user memory")
Cc: stable@...r.kernel.org
Reported-by: Nimish Mishra <neelam.nimish@...il.com>
Reported-by: Anirban Chakraborty <ch.anirban00727@...il.com>
Reported-by: Debdeep Mukhopadhyay <debdeep.mukhopadhyay@...il.com>
Suggested-by: Jerome Forissier <jerome.forissier@...aro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@...aro.org>
---
 drivers/tee/tee_shm.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index f2b1bcefcadd..f71651021c8d 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -231,15 +231,30 @@ EXPORT_SYMBOL_GPL(tee_shm_alloc_priv_buf);
 
 static struct tee_shm *
 register_shm_helper(struct tee_context *ctx, unsigned long addr,
-		    size_t length, u32 flags, int id)
+		    unsigned long length, u32 flags, int id)
 {
 	struct tee_device *teedev = ctx->teedev;
+	unsigned long end_addr;
 	struct tee_shm *shm;
 	unsigned long start;
 	size_t num_pages;
 	void *ret;
 	int rc;
 
+	/* Check for overflows, this may be input from user space */
+	addr = untagged_addr(addr);
+	start = rounddown(addr, PAGE_SIZE);
+	if (check_add_overflow(addr, length, &end_addr))
+		return ERR_PTR(-EINVAL);
+	end_addr = roundup(end_addr, PAGE_SIZE);
+	if (end_addr < start)
+		return ERR_PTR(-EINVAL);
+	num_pages = (end_addr - start) / PAGE_SIZE;
+
+	/* Error out early if no pages are to be registered */
+	if (!num_pages)
+		return ERR_PTR(-EINVAL);
+
 	if (!tee_device_get(teedev))
 		return ERR_PTR(-EINVAL);
 
@@ -261,11 +276,8 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr,
 	shm->flags = flags;
 	shm->ctx = ctx;
 	shm->id = id;
-	addr = untagged_addr(addr);
-	start = rounddown(addr, PAGE_SIZE);
 	shm->offset = addr - start;
 	shm->size = length;
-	num_pages = (roundup(addr + length, PAGE_SIZE) - start) / PAGE_SIZE;
 	shm->pages = kcalloc(num_pages, sizeof(*shm->pages), GFP_KERNEL);
 	if (!shm->pages) {
 		ret = ERR_PTR(-ENOMEM);
@@ -326,6 +338,9 @@ struct tee_shm *tee_shm_register_user_buf(struct tee_context *ctx,
 	void *ret;
 	int id;
 
+	if (!access_ok((void __user *)addr, length))
+		return ERR_PTR(-EFAULT);
+
 	mutex_lock(&teedev->mutex);
 	id = idr_alloc(&teedev->idr, NULL, 1, 0, GFP_KERNEL);
 	mutex_unlock(&teedev->mutex);
-- 
2.31.1

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