iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

s390: always save and restore all registers on context switch

Browse Source 
commit fbbd7f1a51 upstream.

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.

Fixes: fdb6d070ef ("switch_to: dont restore/save access & fpu regs for kernel threads")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Heiko Carstens
2017-11-20 12:38:44 +01:00
committed by Greg Kroah-Hartman
parent b68df97ec8
commit cb90fcfcdd
1 changed files with 13 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

27
arch/s390/include/asm/switch_to.h
View File

@ -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 \
save_fpu_regs(); \ * a restore of the floating point / vector registers as \
save_access_regs(&prev->thread.acrs[0]); \ * soon as the next task returns to user space \
save_ri_cb(prev->thread.ri_cb); \ */ \
save_gs_cb(prev->thread.gs_cb); \ save_fpu_regs(); \
} \ save_access_regs(&prev->thread.acrs[0]); \
save_ri_cb(prev->thread.ri_cb); \
save_gs_cb(prev->thread.gs_cb); \
update_cr_regs(next); \ update_cr_regs(next); \
if (next->mm) { \ restore_access_regs(&next->thread.acrs[0]); \
set_cpu_flag(CIF_FPU); \ restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \
restore_access_regs(&next->thread.acrs[0]); \ restore_gs_cb(next->thread.gs_cb); \
restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \ prev = __switch_to(prev, next); \
restore_gs_cb(next->thread.gs_cb); \
} \
prev = __switch_to(prev,next); \
} while (0) } while (0)
#endif /* __ASM_SWITCH_TO_H */ #endif /* __ASM_SWITCH_TO_H */