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Set %esp correctly in the extended TSS.

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The pcb is saved at the top of the kernel stack on x86 platforms.
The initial kenrel stack pointer is set in the TSS so that the trapframe
from user -> kernel transitions begins directly below the pcb and grows
down.

The XSAVE changes moved the FPU save area out of the pcb and into a
variable-sized area after the pcb.  This required updating the expressions
to calculate the initial stack pointer from 'stacktop - sizeof(pcb)' to
'stacktop - sizeof(pcb) + FPU save area size'.

The i386_set_ioperm() system call allows user applications to access
individual I/O ports via the I/O port permission bitmap in the TSS.
On FreeBSD this requires allocating a custom per-process TSS instead of
using the shared per-CPU TSS.

The expression to initialize the initial kernel stack pointer in the
per-process TSS created for i386_set_ioperm() was not properly updated
after the XSAVE changes.  Processes that used i386_set_ioperm() would
trash the trapframe during subsequent context switches resulting in
panics from memory corruption.

This changes fixes the kernel stack pointer calculation for the per-process
TSS.

Reviewed by:	kib, n_hibma
Reported by:	n_hibma
MFC after:	1 week
This commit is contained in:
John Baldwin 2015-12-07 16:27:11 +00:00
parent 1f0d6c0786
commit d99775308a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=291947
1 changed files with 1 additions and 2 deletions
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3
sys/i386/i386/sys_machdep.c
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@ -275,8 +275,7 @@ i386_extend_pcb(struct thread *td)
ext = (struct pcb_ext *)kmem_malloc(kernel_arena, ctob(IOPAGES+1),
M_WAITOK | M_ZERO);
/* -16 is so we can convert a trapframe into vm86trapframe inplace */
ext->ext_tss.tss_esp0 = td->td_kstack + ctob(td->td_kstack_pages) -
sizeof(struct pcb) - 16;
ext->ext_tss.tss_esp0 = (vm_offset_t)td->td_pcb - 16;
ext->ext_tss.tss_ss0 = GSEL(GDATA_SEL, SEL_KPL);
/*
* The last byte of the i/o map must be followed by an 0xff byte.