linux-kernel - Re: [PATCH] tee: Prevent size calculation wraparound on 32-bit kernels

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Message-ID: <CAHUa44GDwSVwwk0RsyDZAf1Jd6Lbf1sUOzbW0kV3Ehr2MNkYdA@mail.gmail.com>
Date: Wed, 30 Apr 2025 15:00:19 +0200
From: Jens Wiklander <jens.wiklander@...aro.org>
To: Rouven Czerwinski <rouven.czerwinski@...aro.org>
Cc: Jann Horn <jannh@...gle.com>, Sumit Garg <sumit.garg@...nel.org>, 
	op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tee: Prevent size calculation wraparound on 32-bit kernels

On Wed, Apr 30, 2025 at 2:12 PM Rouven Czerwinski
<rouven.czerwinski@...aro.org> wrote:
>
> Hi,
>
> On Wed, 30 Apr 2025 at 13:53, Jens Wiklander <jens.wiklander@...aro.org> wrote:
> >
> > On Mon, Apr 28, 2025 at 3:06 PM Jann Horn <jannh@...gle.com> wrote:
> > >
> > > The current code around TEE_IOCTL_PARAM_SIZE() is a bit wrong on
> > > 32-bit kernels: Multiplying a user-provided 32-bit value with the
> > > size of a structure can wrap around on such platforms.
> > >
> > > Fix it by using saturating arithmetic for the size calculation.
> > >
> > > This has no security consequences because, in all users of
> > > TEE_IOCTL_PARAM_SIZE(), the subsequent kcalloc() implicitly checks
> > > for wrapping.
> > >
> > > Signed-off-by: Jann Horn <jannh@...gle.com>
> > > ---
> > > Note that I don't have a test device with a TEE; I only compile-tested
> > > the change on an x86-64 build.
> > > ---
> > >  drivers/tee/tee_core.c | 11 ++++++-----
> > >  1 file changed, 6 insertions(+), 5 deletions(-)
> >
> > Looks good, I'm picking up this.
> >
> > Thanks,
> > Jens
> >
> > >
> > > diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> > > index d113679b1e2d..acc7998758ad 100644
> > > --- a/drivers/tee/tee_core.c
> > > +++ b/drivers/tee/tee_core.c
> > > @@ -10,6 +10,7 @@
> > >  #include <linux/fs.h>
> > >  #include <linux/idr.h>
> > >  #include <linux/module.h>
> > > +#include <linux/overflow.h>
> > >  #include <linux/slab.h>
> > >  #include <linux/tee_core.h>
> > >  #include <linux/uaccess.h>
> > > @@ -19,7 +20,7 @@
> > >
> > >  #define TEE_NUM_DEVICES        32
> > >
> > > -#define TEE_IOCTL_PARAM_SIZE(x) (sizeof(struct tee_param) * (x))
> > > +#define TEE_IOCTL_PARAM_SIZE(x) (size_mul(sizeof(struct tee_param), (x)))
> > >
> > >  #define TEE_UUID_NS_NAME_SIZE  128
> > >
> > > @@ -487,7 +488,7 @@ static int tee_ioctl_open_session(struct tee_context *ctx,
> > >         if (copy_from_user(&arg, uarg, sizeof(arg)))
> > >                 return -EFAULT;
> > >
> > > -       if (sizeof(arg) + TEE_IOCTL_PARAM_SIZE(arg.num_params) != buf.buf_len)
> > > +       if (size_add(sizeof(arg), TEE_IOCTL_PARAM_SIZE(arg.num_params)) != buf.buf_len)
> > >                 return -EINVAL;
> > >
> > >         if (arg.num_params) {
> > > @@ -565,7 +566,7 @@ static int tee_ioctl_invoke(struct tee_context *ctx,
> > >         if (copy_from_user(&arg, uarg, sizeof(arg)))
> > >                 return -EFAULT;
> > >
> > > -       if (sizeof(arg) + TEE_IOCTL_PARAM_SIZE(arg.num_params) != buf.buf_len)
> > > +       if (size_add(sizeof(arg), TEE_IOCTL_PARAM_SIZE(arg.num_params)) != buf.buf_len)
> > >                 return -EINVAL;
> > >
> > >         if (arg.num_params) {
> > > @@ -699,7 +700,7 @@ static int tee_ioctl_supp_recv(struct tee_context *ctx,
> > >         if (get_user(num_params, &uarg->num_params))
> > >                 return -EFAULT;
> > >
> > > -       if (sizeof(*uarg) + TEE_IOCTL_PARAM_SIZE(num_params) != buf.buf_len)
> > > +       if (size_add(sizeof(*uarg), TEE_IOCTL_PARAM_SIZE(num_params)) != buf.buf_len)
> > >                 return -EINVAL;
> > >
> > >         params = kcalloc(num_params, sizeof(struct tee_param), GFP_KERNEL);
> > > @@ -798,7 +799,7 @@ static int tee_ioctl_supp_send(struct tee_context *ctx,
> > >             get_user(num_params, &uarg->num_params))
> > >                 return -EFAULT;
> > >
> > > -       if (sizeof(*uarg) + TEE_IOCTL_PARAM_SIZE(num_params) > buf.buf_len)
> > > +       if (size_add(sizeof(*uarg), TEE_IOCTL_PARAM_SIZE(num_params)) > buf.buf_len)
> > >                 return -EINVAL;
> > >
> > >         params = kcalloc(num_params, sizeof(struct tee_param), GFP_KERNEL);
> > >
> > > ---
> > > base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e
> > > change-id: 20250428-tee-sizecheck-299d5eff8fc7
> > >
> > > --
> > > Jann Horn <jannh@...gle.com>
> > >
>
> I ran this through the arm32 qemu virt machine to test my new development setup,
> so:
>
> Tested-by: Rouven Czerwinski <rouven.czerwinski@...aro.org>

Thanks for testing.

Cheers,
Jens

>
> Best regards,
> Rouven