[Bug 1879955] Re: target/i386/seg_helper.c: 16-bit TSS struct format wrong?

[Thomas Huth]

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** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1879955

Title:
  target/i386/seg_helper.c: 16-bit TSS struct format wrong?

Status in QEMU:
  Incomplete

Bug description:
  In target/i386/seg_helper.c:switch_tss_ra() we have the following code
  to load registers from a 16-bit TSS struct:

          /* 16 bit */
          new_cr3 = 0;
          new_eip = cpu_lduw_kernel_ra(env, tss_base + 0x0e, retaddr);
          new_eflags = cpu_lduw_kernel_ra(env, tss_base + 0x10, retaddr);
          for (i = 0; i < 8; i++) {
              new_regs[i] = cpu_lduw_kernel_ra(env, tss_base + (0x12 + i * 2),
                                               retaddr) | 0xffff0000;
          }
          for (i = 0; i < 4; i++) {
              new_segs[i] = cpu_lduw_kernel_ra(env, tss_base + (0x22 + i * 4),
                                               retaddr);
          }
          new_ldt = cpu_lduw_kernel_ra(env, tss_base + 0x2a, retaddr);

  This doesn't match up with the structure described here:
  https://www.sandpile.org/x86/tss.htm -- which has only 2-byte slots
  for the segment registers. It also makes the 3rd segreg use the same
  offset as the LDTR, which is very suspicious. I suspect that this
  should use "(0x22 + i * 2)".

  The code later in the same function that stores the segment registers
  to the struct has the same bug.

  Found by code inspection; I don't have a test case to check this. As a
  non-x86-expert I'm just going to file a bug report in case somebody
  else feels like confirming the issue and sending a patch.

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