Date: Tue, 27 Sep 2016 15:35:17 -0700 From: "LeMay, Michael" <michael.lemay@...el.com> To: "musl@...ts.openwall.com" <musl@...ts.openwall.com> Subject: [RFC PATCH 2/7] avoid invoking the vDSO when SafeStack is enabled The Linux vDSO code may be incompatible with programs that enable segmentation-hardened SafeStack. This patch prevents the vDSO from being invoked when segmentation-hardened SafeStack is enabled. Signed-off-by: Michael LeMay <michael.lemay@...el.com> --- arch/i386/syscall_arch.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/i386/syscall_arch.h b/arch/i386/syscall_arch.h index 4c9d874..08e0910 100644 --- a/arch/i386/syscall_arch.h +++ b/arch/i386/syscall_arch.h @@ -52,8 +52,21 @@ static inline long __syscall6(long n, long a1, long a2, long a3, long a4, long a return __ret; } +#if !SAFE_STACK +/* The vDSO is not compiled with segmentation-hardened SafeStack. Avoid + * invoking the vDSO when hardened SafeStack is enabled, since it may try to + * access the stack using memory operands with base registers other than EBP or + * ESP without also using a stack segment override prefix. A special compiler + * pass needs to be used to add such prefixes, and it is unlikely that a pass + * of that sort was applied when the vDSO was compiled. + * + * A possible alternative to disabling the use of the vDSO may be to load the + * default flat data segment into DS prior to invoking the vDSO and reloading + * the restricted data segment into DS after the vDSO routine returns. + */ #define VDSO_USEFUL #define VDSO_CGT_SYM "__vdso_clock_gettime" #define VDSO_CGT_VER "LINUX_2.6" +#endif #define SYSCALL_USE_SOCKETCALL -- 2.7.4
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