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[PATCH v8 20/28] x86/insn-eval: Handle 32-bit address encodings in virtual-8086 mode

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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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[PATCH v8 00/28] x86: Enable User-Mode Instruction Prevention Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:30 +0200
  [PATCH v8 18/28] x86/insn-eval: Add support to resolve 32-bit address encodings Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:30 +0200
  [PATCH v8 04/28] uprobes/x86: Use existing definitions for segment override prefixes Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:30 +0200
  [PATCH v8 17/28] x86/insn-eval: Incorporate segment base in linear address computation Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:30 +0200
  [PATCH v8 08/28] x86/mpx, x86/insn: Relocate insn util functions to a new insn-eval file Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:30 +0200
  [PATCH v8 10/28] x86/insn-eval: Add a utility function to get register offsets Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:30 +0200
  [PATCH v8 19/28] x86/insn-eval: Add wrapper function for 32 and 64-bit addresses Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 20/28] x86/insn-eval: Handle 32-bit address encodings in virtual-8086 mode Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 15/28] x86/insn-eval: Add function to get default params of code segment Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 05/28] x86/mpx: Use signed variables to compute effective addresses Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 16/28] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 101b Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 13/28] x86/insn-eval: Add utility function to get segment descriptor Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 03/28] ptrace,x86: Make user_64bit_mode() available to 32-bit builds Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 23/28] x86: Add emulation code for UMIP instructions Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 28/28] selftests/x86: Add tests for instruction str and sldt Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 21/28] x86/insn-eval: Add support to resolve 16-bit addressing encodings Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 12/28] x86/insn-eval: Add utility functions to get segment selector Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 01/28] x86/mm: Relocate page fault error codes to traps.h Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 27/28] selftests/x86: Add tests for User-Mode Instruction Prevention Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 24/28] x86/umip: Force a page fault when unable to copy emulated result to user Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 26/28] x86/traps: Fixup general protection faults caused by UMIP Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 07/28] x86/mpx: Do not use SIB.base if its value is 101b and ModRM.mod = 0 Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 22/28] x86/cpufeature: Add User-Mode Instruction Prevention definitions Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 06/28] x86/mpx: Do not use SIB.index if its value is 100b and ModRM.mod is not 11b Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 14/28] x86/insn-eval: Add utility functions to get segment descriptor base address and limit Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 25/28] x86: Enable User-Mode Instruction Prevention Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200
  [PATCH v8 09/28] x86/insn-eval: Do not BUG on invalid register type Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-08-19 02:40 +0200

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