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CVE-2018-8897: Debug Exception May Cause Unexpected Behavior

A statement in the System Programming Guide of the Intel 64 and IA-32 Architectures Software Developer’s Manual (SDM) was mishandled in the development of some or all operating-system kernels, resulting in unexpected behavior for #DB exceptions that are deferred by MOV SS or POP SS, as demonstrated by (for example) privilege escalation in Windows, macOS, some Xen configurations, or FreeBSD, or a Linux kernel crash. The MOV to SS and POP SS instructions inhibit interrupts (including NMIs), data breakpoints, and single step trap exceptions until the instruction boundary following the next instruction (SDM Vol. 3A; section 6.8.3). (The inhibited data breakpoints are those on memory accessed by the MOV to SS or POP to SS instruction itself.) Note that debug exceptions are not inhibited by the interrupt enable (EFLAGS.IF) system flag (SDM Vol. 3A; section 2.3). If the instruction following the MOV to SS or POP to SS instruction is an instruction like SYSCALL, SYSENTER, INT 3, etc. that transfers control to the operating system at CPL < 3, the debug exception is delivered after the transfer to CPL < 3 is complete. OS kernels may not expect this order of events and may therefore experience unexpected behavior when it occurs.

https://www.triplefault.io/2018/05/spurious-db-exceptions-with-pop-ss.html
https://everdox.net/popss.pdf

https://software.intel.com/en-us/articles/intel-sdm

https://www.kb.cert.org/vuls/id/631579
https://nvd.nist.gov/vuln/detail/CVE-2018-8897
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-8897
http://openwall.com/lists/oss-security/2018/05/08/1
http://openwall.com/lists/oss-security/2018/05/08/4

https://github.com/torvalds/linux/commit/d8ba61ba58c88d5207c1ba2f7d9a2280e7d03be9
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d8ba61ba58c88d5207c1ba2f7d9a2280e7d03be9
https://patchwork.kernel.org/patch/10386677/
https://people.canonical.com/~ubuntu-security/cve/2018/CVE-2018-8897.html
https://security-tracker.debian.org/tracker/CVE-2018-8897
https://kb.vmware.com/s/article/54988
https://bugzilla.redhat.com/show_bug.cgi?id=1567074
https://support.apple.com/HT208742
https://svnweb.freebsd.org/base?view=revision&revision=333368
https://www.freebsd.org/security/advisories/FreeBSD-SA-18:06.debugreg.asc
https://xenbits.xen.org/xsa/advisory-260.html
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2018-8897

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