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[Bug 1503031] Re: 32-to-64-bit call gate unsupported in IA32e mode
From: |
Peter Maydell |
Subject: |
[Bug 1503031] Re: 32-to-64-bit call gate unsupported in IA32e mode |
Date: |
Fri, 07 Aug 2020 18:59:33 -0000 |
Looking at the commit log it looks like Andrew fixed this in commit
0aca060526d3ff9632aaed in 2018 ?
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https://bugs.launchpad.net/bugs/1503031
Title:
32-to-64-bit call gate unsupported in IA32e mode
Status in QEMU:
Incomplete
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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