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| author | Christian Krinitsin <mail@krinitsin.com> | 2025-06-30 12:34:26 +0000 |
|---|---|---|
| committer | Christian Krinitsin <mail@krinitsin.com> | 2025-06-30 12:35:44 +0000 |
| commit | 25f8033d556aa17afaea4a5196ea7a69fe248320 (patch) | |
| tree | 0f056db167683be54ea1e5e72d29d6069af55e7d /results/classifier/deepseek-2-tmp/output/hypervisor/1428352 | |
| parent | 8e6da29e4ee5fc14bc1cc816a24f21271f14090d (diff) | |
| download | qemu-analysis-25f8033d556aa17afaea4a5196ea7a69fe248320.tar.gz qemu-analysis-25f8033d556aa17afaea4a5196ea7a69fe248320.zip | |
add new temporary deepseek-r1:14b results
Diffstat (limited to 'results/classifier/deepseek-2-tmp/output/hypervisor/1428352')
| -rw-r--r-- | results/classifier/deepseek-2-tmp/output/hypervisor/1428352 | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/results/classifier/deepseek-2-tmp/output/hypervisor/1428352 b/results/classifier/deepseek-2-tmp/output/hypervisor/1428352 new file mode 100644 index 000000000..c4dd6358c --- /dev/null +++ b/results/classifier/deepseek-2-tmp/output/hypervisor/1428352 @@ -0,0 +1,45 @@ + +SYSRET instruction incorrectly implemented + +The Intel architecture manual states that when returning to user mode, the SYSRET instruction will re-load the stack selector (%ss) from the IA32_STAR model specific register using the following logic: + +SS.Selector <-- (IA32_STAR[63:48]+8) OR 3; (* RPL forced to 3 *) + +Another description of the instruction behavior which shows the same logic in a slightly different form can also be found here: + +http://tptp.cc/mirrors/siyobik.info/instruction/SYSRET.html + +[...] + SS(SEL) = IA32_STAR[63:48] + 8; + SS(PL) = 0x3; +[...] + +In other words, the value of the %ss register is supposed to be loaded from bits 63:48 of the IA32_STAR model-specific register, incremented by 8, and then ORed with 3. ORing in the 3 sets the privilege level to 3 (user). This is done since SYSRET returns to user mode after a system call. + +However, helper_sysret() in target-i386/seg_helper.c does not do the "OR 3" step. The code looks like this: + + cpu_x86_load_seg_cache(env, R_SS, selector + 8, + 0, 0xffffffff, + DESC_G_MASK | DESC_B_MASK | DESC_P_MASK | + DESC_S_MASK | (3 << DESC_DPL_SHIFT) | + DESC_W_MASK | DESC_A_MASK); + +It should look like this: + + cpu_x86_load_seg_cache(env, R_SS, (selector + 8) | 3, + 0, 0xffffffff, + DESC_G_MASK | DESC_B_MASK | DESC_P_MASK | + DESC_S_MASK | (3 << DESC_DPL_SHIFT) | + DESC_W_MASK | DESC_A_MASK); + +The code does correctly set the privilege level bits for the code selector register (%cs) but not for the stack selector (%ss). + +The effect of this is that when SYSRET returns control to the user-mode caller, %ss will be have the privilege level bits cleared. In my case, it went from 0x2b to 0x28. This caused a crash later: when the user-mode code was preempted by an interrupt, and the interrupt handler would do an IRET, a general protection fault would occur because the %ss value being loaded from the exception frame was not valid for user mode. (At least, I think that's what happened.) + +This behavior seems inconsistent with real hardware, and also appears to be wrong with respect to the Intel documentation, so I'm pretty confident in calling this a bug. :) + +Note that this issue seems to have been around for a long time. I discovered it while using QEMU 2.2.0, but I happened to have the sources for QEMU 0.10.5, and the problem is there too (in os_helper.c). I am using FreeBSD/amd64 9.1-RELEASE as my host system, without KVM. + +The fix is fairly simple. I'm attaching a patch which worked for me. Using this fix, the code that I'm testing now behaves the same on the QEMU virtual machine as on real hardware. + +- Bill (<email address hidden>) \ No newline at end of file |