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    Subject[PATCH v8 20/28] x86/insn-eval: Handle 32-bit address encodings in virtual-8086 mode
    Date
    It is possible to utilize 32-bit address encodings in virtual-8086 mode via
    an address override instruction prefix. However, the range of the
    effective address is still limited to [0x-0xffff]. In such a case, return
    error.

    Also, linear addresses in virtual-8086 mode are limited to 20 bits. Enforce
    such limit by truncating the most significant bytes of the computed linear
    address.

    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
    Cc: Colin Ian King <colin.king@canonical.com>
    Cc: Lorenzo Stoakes <lstoakes@gmail.com>
    Cc: Qiaowei Ren <qiaowei.ren@intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Thomas Garnier <thgarnie@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
    Cc: x86@kernel.org
    Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    ---
    arch/x86/lib/insn-eval.c | 11 +++++++++++
    1 file changed, 11 insertions(+)

    diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
    index 6537b613d0b3..93a6d1f57c2d 100644
    --- a/arch/x86/lib/insn-eval.c
    +++ b/arch/x86/lib/insn-eval.c
    @@ -801,12 +801,23 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs)
    goto out_err;

    /*
    + * Even though 32-bit address encodings are allowed in virtual-8086
    + * mode, the address range is still limited to [0x-0xffff].
    + */
    + if (v8086_mode(regs) && (eff_addr & ~0xffff))
    + goto out_err;
    +
    + /*
    * Data type long could be 64 bits in size. Ensure that our 32-bit
    * effective address is not sign-extended when computing the linear
    * address.
    */
    linear_addr = (unsigned long)(eff_addr & 0xffffffff) + seg_base_addr;

    + /* Limit linear address to 20 bits */
    + if (v8086_mode(regs))
    + linear_addr &= 0xfffff;
    +
    return (void __user *)linear_addr;
    out_err:
    return (void __user *)-1L;
    --
    2.13.0
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