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x86/cpu: Adjust reset_stack_and_jump() to be shadow stack compatible
We need to unwind up to the supervisor token. See the comment for details. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>
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Andrew Cooper committed
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commit
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1 file changed
+45
-3
@@ -124,13 +124,55 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
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# define CHECK_FOR_LIVEPATCH_WORK ""
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#endif
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#ifdef CONFIG_XEN_SHSTK
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/*
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* We need to unwind the primary shadow stack to its supervisor token, located
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* in the last word of the primary shadow stack.
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*
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* Read the shadow stack pointer, subtract it from supervisor token position,
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* and divide by 8 to get the number of slots needing popping.
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*
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* INCSSPQ can't pop more than 255 entries. We shouldn't ever need to pop
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* that many entries, and getting this wrong will cause us to #DF later. Turn
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* it into a BUG() now for fractionally easier debugging.
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*/
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# define SHADOW_STACK_WORK \
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"mov $1, %[ssp];" \
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"rdsspd %[ssp];" \
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"cmp $1, %[ssp];" \
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"je .L_shstk_done.%=;" /* CET not active? Skip. */ \
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"mov $%c[skstk_base], %[val];" \
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"and $%c[stack_mask], %[ssp];" \
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"sub %[ssp], %[val];" \
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"shr $3, %[val];" \
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"cmp $255, %[val];" /* More than 255 entries? Crash. */ \
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UNLIKELY_START(a, shstk_adjust) \
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_ASM_BUGFRAME_TEXT(0) \
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UNLIKELY_END_SECTION ";" \
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"incsspq %q[val];" \
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".L_shstk_done.%=:"
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#else
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# define SHADOW_STACK_WORK ""
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#endif
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#define switch_stack_and_jump(fn, instr) \
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({ \
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unsigned int tmp; \
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__asm__ __volatile__ ( \
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"mov %0,%%"__OP"sp;" \
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SHADOW_STACK_WORK \
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"mov %[stk], %%rsp;" \
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instr \
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"jmp %c1" \
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: : "r" (guest_cpu_user_regs()), "i" (fn) : "memory" ); \
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"jmp %c[fun];" \
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: [val] "=&r" (tmp), \
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[ssp] "=&r" (tmp) \
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: [stk] "r" (guest_cpu_user_regs()), \
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[fun] "i" (fn), \
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[skstk_base] "i" \
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((PRIMARY_SHSTK_SLOT + 1) * PAGE_SIZE - 8), \
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[stack_mask] "i" (STACK_SIZE - 1), \
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_ASM_BUGFRAME_INFO(BUGFRAME_bug, __LINE__, \
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__FILE__, NULL) \
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: "memory" ); \
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unreachable(); \
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})
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