linux-kernel - Re: [PATCH] powerpc: check previous kernel's ima-kexec-buffer against memory bounds

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Message-ID: <87k0agmq12.fsf@mpe.ellerman.id.au>
Date:   Fri, 20 May 2022 20:55:53 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Vaibhav Jain <vaibhav@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Frank Rowand <frowand.list@...il.com>,
        Prakhar Srivastava <prsriva@...ux.microsoft.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH] powerpc: check previous kernel's ima-kexec-buffer
 against memory bounds

Vaibhav Jain <vaibhav@...ux.ibm.com> writes:
>
> [PATCH] powerpc: check previous kernel's ima-kexec-buffer against memory bounds

This isn't a powerpc patch, the subject should start with "of:".

> Presently ima_get_kexec_buffer() doesn't check if the previous kernel's
> ima-kexec-buffer lies outside the addressable memory range. This can result
> in a kernel panic if the new kernel is booted with 'mem=X' arg and the
> ima-kexec-buffer was allocated beyond that range by the previous kernel.
> The panic is usually of the form below:
>
> $ sudo kexec --initrd initrd vmlinux --append='mem=16G'
>
> <snip>
>  BUG: Unable to handle kernel data access on read at 0xc000c01fff7f0000
>  Faulting instruction address: 0xc000000000837974
>  Oops: Kernel access of bad area, sig: 11 [#1]
> <snip>
>  NIP [c000000000837974] ima_restore_measurement_list+0x94/0x6c0
>  LR [c00000000083b55c] ima_load_kexec_buffer+0xac/0x160
>  Call Trace:
>  [c00000000371fa80] [c00000000083b55c] ima_load_kexec_buffer+0xac/0x160
>  [c00000000371fb00] [c0000000020512c4] ima_init+0x80/0x108
>  [c00000000371fb70] [c0000000020514dc] init_ima+0x4c/0x120
>  [c00000000371fbf0] [c000000000012240] do_one_initcall+0x60/0x2c0
>  [c00000000371fcc0] [c000000002004ad0] kernel_init_freeable+0x344/0x3ec
>  [c00000000371fda0] [c0000000000128a4] kernel_init+0x34/0x1b0
>  [c00000000371fe10] [c00000000000ce64] ret_from_kernel_thread+0x5c/0x64
>  Instruction dump:
>  f92100b8 f92100c0 90e10090 910100a0 4182050c 282a0017 3bc00000 40810330
>  7c0802a6 fb610198 7c9b2378 f80101d0 <a1240000> 2c090001 40820614 e9240010
>  ---[ end trace 0000000000000000 ]---
>
> Fix this issue by checking returned address/size of previous kernel's
> ima-kexec-buffer against memblock's memory bounds.
>
> Fixes: fee3ff99bc67("powerpc: Move arch independent ima kexec functions to
> drivers/of/kexec.c")
>
> Cc: Frank Rowand <frowand.list@...il.com>
> Cc: Prakhar Srivastava <prsriva@...ux.microsoft.com>
> Cc: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
> Cc: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
> Cc: Rob Herring <robh@...nel.org>
> Signed-off-by: Vaibhav Jain <vaibhav@...ux.ibm.com>
> ---
>  drivers/of/kexec.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> index b9bd1cff1793..c73007eda52d 100644
> --- a/drivers/of/kexec.c
> +++ b/drivers/of/kexec.c
> @@ -140,6 +140,13 @@ int ima_get_kexec_buffer(void **addr, size_t *size)
>  	if (ret)
>  		return ret;
>  
> +	/* if the ima-kexec-buffer goes beyond the addressable memory */
> +	if (!memblock_is_region_memory(tmp_addr, tmp_size)) {

Not all arches keep the memblock info around after boot.

I think this will be called too late, but I'd have to check the exact
timing to be sure.

I think you can use pfn_valid() instead?

cheers

> +		pr_warn("IMA buffer at 0x%lx, size = 0x%zx beyond memory\n",
> +			tmp_addr, tmp_size);
> +		return -EINVAL;
> +	}
> +
>  	*addr = __va(tmp_addr);
>  	*size = tmp_size;
>  
> -- 
> 2.35.1