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    Subject[PATCH v7 1/6] of: check previous kernel's ima-kexec-buffer against memory bounds
    Date
    From: Vaibhav Jain <vaibhav@linux.ibm.com>

    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 PFN range of previous kernel's
    ima-kexec-buffer with page_is_ram() to ensure correct memory bounds.

    Fixes: 467d27824920 ("powerpc: ima: get the kexec buffer passed by the previous kernel")
    Cc: Frank Rowand <frowand.list@gmail.com>
    Cc: Prakhar Srivastava <prsriva@linux.microsoft.com>
    Cc: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
    Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
    Cc: Rob Herring <robh@kernel.org>
    Cc: Ritesh Harjani <ritesh.list@gmail.com>
    Cc: Robin Murphy <robin.murphy@arm.com>
    Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
    Signed-off-by: Rob Herring <robh@kernel.org>
    Link: https://lore.kernel.org/r/20220531041446.3334259-1-vaibhav@linux.ibm.com
    ---
    drivers/of/kexec.c | 17 +++++++++++++++++
    1 file changed, 17 insertions(+)

    diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
    index 8d374cc552be..91b04b04eec4 100644
    --- a/drivers/of/kexec.c
    +++ b/drivers/of/kexec.c
    @@ -126,6 +126,7 @@ int ima_get_kexec_buffer(void **addr, size_t *size)
    {
    int ret, len;
    unsigned long tmp_addr;
    + unsigned long start_pfn, end_pfn;
    size_t tmp_size;
    const void *prop;

    @@ -140,6 +141,22 @@ int ima_get_kexec_buffer(void **addr, size_t *size)
    if (ret)
    return ret;

    + /* Do some sanity on the returned size for the ima-kexec buffer */
    + if (!tmp_size)
    + return -ENOENT;
    +
    + /*
    + * Calculate the PFNs for the buffer and ensure
    + * they are with in addressable memory.
    + */
    + start_pfn = PHYS_PFN(tmp_addr);
    + end_pfn = PHYS_PFN(tmp_addr + tmp_size - 1);
    + if (!page_is_ram(start_pfn) || !page_is_ram(end_pfn)) {
    + 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
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