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tcg: Introduce set/clear_helper_retaddr

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At present we have a potential error in that helper_retaddr contains
data for handle_cpu_signal, but we have not ensured that those stores
will be scheduled properly before the operation that may fault.

It might be that these races are not in practice observable, due to
our use of -fno-strict-aliasing, but better safe than sorry.

Adjust all of the setters of helper_retaddr.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2019-06-13 15:54:22 -07:00
parent 359896dfa4
commit 08b97f7ff2
5 changed files with 57 additions and 37 deletions
Download patch file Download diff file Expand all files Collapse all files

20
include/exec/cpu_ldst.h
View file

@ -89,6 +89,26 @@ typedef target_ulong abi_ptr;
extern __thread uintptr_t helper_retaddr;
static inline void set_helper_retaddr(uintptr_t ra)
{
helper_retaddr = ra;
/*
* Ensure that this write is visible to the SIGSEGV handler that
* may be invoked due to a subsequent invalid memory operation.
*/
signal_barrier();
}
static inline void clear_helper_retaddr(void)
{
/*
* Ensure that previous memory operations have succeeded before
* removing the data visible to the signal handler.
*/
signal_barrier();
helper_retaddr = 0;
}
/* In user-only mode we provide only the _code and _data accessors. */
#define MEMSUFFIX _data

12
include/exec/cpu_ldst_useronly_template.h
View file

@ -78,9 +78,9 @@ glue(glue(glue(cpu_ld, USUFFIX), MEMSUFFIX), _ra)(CPUArchState *env,
uintptr_t retaddr)
{
RES_TYPE ret;
helper_retaddr = retaddr;
set_helper_retaddr(retaddr);
ret = glue(glue(cpu_ld, USUFFIX), MEMSUFFIX)(env, ptr);
helper_retaddr = 0;
clear_helper_retaddr();
return ret;
}
@ -102,9 +102,9 @@ glue(glue(glue(cpu_lds, SUFFIX), MEMSUFFIX), _ra)(CPUArchState *env,
uintptr_t retaddr)
{
int ret;
helper_retaddr = retaddr;
set_helper_retaddr(retaddr);
ret = glue(glue(cpu_lds, SUFFIX), MEMSUFFIX)(env, ptr);
helper_retaddr = 0;
clear_helper_retaddr();
return ret;
}
#endif
@ -128,9 +128,9 @@ glue(glue(glue(cpu_st, SUFFIX), MEMSUFFIX), _ra)(CPUArchState *env,
RES_TYPE v,
uintptr_t retaddr)
{
helper_retaddr = retaddr;
set_helper_retaddr(retaddr);
glue(glue(cpu_st, SUFFIX), MEMSUFFIX)(env, ptr, v);
helper_retaddr = 0;
clear_helper_retaddr();
}
#endif