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

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Message-ID: <CAK8z29XWCujUdLXcHz075+xcix8HV2Mp3EtxxX9GB7vGjwi3HA@mail.gmail.com>
Date: Wed, 30 Apr 2025 14:12:28 +0200
From: Rouven Czerwinski <rouven.czerwinski@...aro.org>
To: Jens Wiklander <jens.wiklander@...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

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>

Best regards,
Rouven