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

[Peter Maydell]

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.

[Thomas Huth (th-huth)]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.

[Thomas Huth (th-huth)]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/382