Date: Mon, 21 Dec 2015 22:16:09 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r292572 - stable/10/sys/i386/i386 Message-ID: <201512212216.tBLMG9pr026699@repo.freebsd.org>
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Author: jhb Date: Mon Dec 21 22:16:09 2015 New Revision: 292572 URL: https://svnweb.freebsd.org/changeset/base/292572 Log: MFC 291947: Set %esp correctly in the extended TSS. 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. Modified: stable/10/sys/i386/i386/sys_machdep.c Directory Properties: stable/10/ (props changed) Modified: stable/10/sys/i386/i386/sys_machdep.c ============================================================================== --- stable/10/sys/i386/i386/sys_machdep.c Mon Dec 21 21:40:15 2015 (r292571) +++ stable/10/sys/i386/i386/sys_machdep.c Mon Dec 21 22:16:09 2015 (r292572) @@ -304,8 +304,7 @@ 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(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.
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