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[Bug 1503031] Re: 32-to-64-bit call gate unsupported in IA32e mode
From: |
Thomas Huth |
Subject: |
[Bug 1503031] Re: 32-to-64-bit call gate unsupported in IA32e mode |
Date: |
Sat, 08 Aug 2020 08:09:21 -0000 |
That looks like the corresponding fix, indeed. Let's close this ticket.
** Changed in: qemu
Status: Incomplete => Fix Released
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https://bugs.launchpad.net/bugs/1503031
Title:
32-to-64-bit call gate unsupported in IA32e mode
Status in QEMU:
Fix Released
Bug description:
In particular, the lcall implementation doesn't support the 64-bit
TSS.
helper_lcall_protected (target-i386/seg_helper.c:1884) calls
get_ss_esp_from_tss() on a call gate to a lower privilege level, which
tries to extract a 32-bit ESP and 16-bit SS from the TSS. In IA32e
mode (64-bit or compatibility mode), this instead grabs the lower
32-bits of the target RSP, and 16 of the upper bits as the SS.
Additionally, several of the subsequent checks are incorrect (even if
the correct stack pointer were extracted).
This isn't a problem for interrupts since the interrupts are given
their own implementation entirely, that uses get_rsp_from_tss() rather
than get_ss_esp_from_tss().
I believe the missing logic is from the branch starting "ELSE (*
current TSS is 64-bit *)" in the CALL pseudocode in the Intel manual
(page 3-124 of the PDF I have).
Reproduced at master (c0b520dfb8890294a9f8879f4759172900585995), and
also as of a qemu built a year ago.
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