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

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Message-Id: <20220518200547.655788-1-vaibhav@linux.ibm.com>
Date:   Thu, 19 May 2022 01:35:47 +0530
From:   Vaibhav Jain <vaibhav@...ux.ibm.com>
To:     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: [PATCH] powerpc: check previous kernel's ima-kexec-buffer against memory bounds

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)) {
+		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