Date: Thu, 29 May 2014 16:18:31 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r266846 - head/sys/amd64/amd64 Message-ID: <201405291618.s4TGIV0R085167@svn.freebsd.org>
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Author: kib Date: Thu May 29 16:18:31 2014 New Revision: 266846 URL: http://svnweb.freebsd.org/changeset/base/266846 Log: When usermode loaded non-default segment selector into the %gs, correctly prepare KGSBASE msr to restore the user descriptor base on the last swapgs during return to usermode. Reported and tested by: peterj Sponsored by: The FreeBSD Foundation MFC after: 1 week Modified: head/sys/amd64/amd64/exception.S Modified: head/sys/amd64/amd64/exception.S ============================================================================== --- head/sys/amd64/amd64/exception.S Thu May 29 16:03:08 2014 (r266845) +++ head/sys/amd64/amd64/exception.S Thu May 29 16:18:31 2014 (r266846) @@ -721,21 +721,38 @@ ld_fsbase: pushfq cli movl $MSR_GSBASE,%ecx + /* Save current kernel %gs base into %r12d:%r13d */ rdmsr + movl %eax,%r12d + movl %edx,%r13d .globl ld_gs ld_gs: movw %si,%gs + /* Save user %gs base into %r14d:%r15d */ + rdmsr + movl %eax,%r14d + movl %edx,%r15d + /* Restore kernel %gs base */ + movl %r12d,%eax + movl %r13d,%edx wrmsr popfq + /* + * Restore user %gs base, either from PCB if used for TLS, or + * from the previously saved msr read. + */ + movl $MSR_KGSBASE,%ecx cmpw $KUG32SEL,%si jne 1f - movl $MSR_KGSBASE,%ecx movl PCB_GSBASE(%r8),%eax movl PCB_GSBASE+4(%r8),%edx + jmp ld_gsbase +1: + movl %r14d,%eax + movl %r15d,%edx .globl ld_gsbase ld_gsbase: - wrmsr -1: + wrmsr /* May trap if non-canonical, but only for TLS. */ .globl ld_es ld_es: movw TF_ES(%rsp),%es
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