Commit fbbd7f1a authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky

s390: always save and restore all registers on context switch

The switch_to() macro has an optimization to avoid saving and
restoring register contents that aren't needed for kernel threads.

There is however the possibility that a kernel thread execve's a user
space program. In such a case the execve'd process can partially see
the contents of the previous process, which shouldn't be allowed.

To avoid this, simply always save and restore register contents on
context switch.

Cc: <stable@vger.kernel.org> # v2.6.37+
Fixes: fdb6d070 ("switch_to: dont restore/save access & fpu regs for kernel threads")
Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent bd7a9b37
...@@ -30,21 +30,20 @@ static inline void restore_access_regs(unsigned int *acrs) ...@@ -30,21 +30,20 @@ static inline void restore_access_regs(unsigned int *acrs)
asm volatile("lam 0,15,%0" : : "Q" (*(acrstype *)acrs)); asm volatile("lam 0,15,%0" : : "Q" (*(acrstype *)acrs));
} }
#define switch_to(prev,next,last) do { \ #define switch_to(prev, next, last) do { \
if (prev->mm) { \ /* save_fpu_regs() sets the CIF_FPU flag, which enforces \
* a restore of the floating point / vector registers as \
* soon as the next task returns to user space \
*/ \
save_fpu_regs(); \ save_fpu_regs(); \
save_access_regs(&prev->thread.acrs[0]); \ save_access_regs(&prev->thread.acrs[0]); \
save_ri_cb(prev->thread.ri_cb); \ save_ri_cb(prev->thread.ri_cb); \
save_gs_cb(prev->thread.gs_cb); \ save_gs_cb(prev->thread.gs_cb); \
} \
update_cr_regs(next); \ update_cr_regs(next); \
if (next->mm) { \
set_cpu_flag(CIF_FPU); \
restore_access_regs(&next->thread.acrs[0]); \ restore_access_regs(&next->thread.acrs[0]); \
restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \ restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \
restore_gs_cb(next->thread.gs_cb); \ restore_gs_cb(next->thread.gs_cb); \
} \ prev = __switch_to(prev, next); \
prev = __switch_to(prev,next); \
} while (0) } while (0)
#endif /* __ASM_SWITCH_TO_H */ #endif /* __ASM_SWITCH_TO_H */
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