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X-Received-From: 2607:f8b0:4864:20::d43 Subject: Re: [Qemu-devel] [PATCH 2/5] tcg: Introduce set/clear_helper_retaddr X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: lvivier@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/9/19 12:07 PM, Alex Bennée wrote: > > Richard Henderson writes: > >> 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. >> >> Signed-off-by: Richard Henderson >> --- >> include/exec/cpu_ldst.h | 20 +++++++++++ >> include/exec/cpu_ldst_useronly_template.h | 12 +++---- >> accel/tcg/user-exec.c | 11 +++--- >> target/arm/helper-a64.c | 8 ++--- >> target/arm/sve_helper.c | 43 +++++++++++------------ >> 5 files changed, 57 insertions(+), 37 deletions(-) >> >> diff --git a/include/exec/cpu_ldst.h b/include/exec/cpu_ldst.h >> index a08b11bd2c..9de8c93303 100644 >> --- a/include/exec/cpu_ldst.h >> +++ b/include/exec/cpu_ldst.h >> @@ -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 >> diff --git a/include/exec/cpu_ldst_useronly_template.h b/include/exec/cpu_ldst_useronly_template.h >> index bc45e2b8d4..e65733f7e2 100644 >> --- a/include/exec/cpu_ldst_useronly_template.h >> +++ b/include/exec/cpu_ldst_useronly_template.h >> @@ -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 >> >> diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c >> index cb5f4b19c5..4384b59a4d 100644 >> --- a/accel/tcg/user-exec.c >> +++ b/accel/tcg/user-exec.c >> @@ -134,7 +134,7 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info, >> * currently executing TB was modified and must be exited >> * immediately. Clear helper_retaddr for next execution. >> */ >> - helper_retaddr = 0; >> + clear_helper_retaddr(); >> cpu_exit_tb_from_sighandler(cpu, old_set); >> /* NORETURN */ >> >> @@ -152,7 +152,7 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info, >> * an exception. Undo signal and retaddr state prior to longjmp. >> */ >> sigprocmask(SIG_SETMASK, old_set, NULL); >> - helper_retaddr = 0; >> + clear_helper_retaddr(); >> >> cc = CPU_GET_CLASS(cpu); >> access_type = is_write ? MMU_DATA_STORE : MMU_DATA_LOAD; >> @@ -682,14 +682,15 @@ static void *atomic_mmu_lookup(CPUArchState *env, target_ulong addr, >> if (unlikely(addr & (size - 1))) { >> cpu_loop_exit_atomic(env_cpu(env), retaddr); >> } >> - helper_retaddr = retaddr; >> - return g2h(addr); >> + void *ret = g2h(addr); >> + set_helper_retaddr(retaddr); >> + return ret; >> } >> >> /* Macro to call the above, with local variables from the use context. */ >> #define ATOMIC_MMU_DECLS do {} while (0) >> #define ATOMIC_MMU_LOOKUP atomic_mmu_lookup(env, addr, DATA_SIZE, GETPC()) >> -#define ATOMIC_MMU_CLEANUP do { helper_retaddr = 0; } while (0) >> +#define ATOMIC_MMU_CLEANUP do { clear_helper_retaddr(); } while (0) >> >> #define ATOMIC_NAME(X) HELPER(glue(glue(atomic_ ## X, SUFFIX), END)) >> #define EXTRA_ARGS >> diff --git a/target/arm/helper-a64.c b/target/arm/helper-a64.c >> index 44e45a8037..060699b901 100644 >> --- a/target/arm/helper-a64.c >> +++ b/target/arm/helper-a64.c >> @@ -554,7 +554,7 @@ uint64_t HELPER(paired_cmpxchg64_le)(CPUARMState *env, uint64_t addr, >> /* ??? Enforce alignment. */ >> uint64_t *haddr = g2h(addr); >> >> - helper_retaddr = ra; >> + set_helper_retaddr(ra); >> o0 = ldq_le_p(haddr + 0); >> o1 = ldq_le_p(haddr + 1); >> oldv = int128_make128(o0, o1); >> @@ -564,7 +564,7 @@ uint64_t HELPER(paired_cmpxchg64_le)(CPUARMState *env, uint64_t addr, >> stq_le_p(haddr + 0, int128_getlo(newv)); >> stq_le_p(haddr + 1, int128_gethi(newv)); >> } >> - helper_retaddr = 0; >> + clear_helper_retaddr(); >> #else >> int mem_idx = cpu_mmu_index(env, false); >> TCGMemOpIdx oi0 = make_memop_idx(MO_LEQ | MO_ALIGN_16, mem_idx); >> @@ -624,7 +624,7 @@ uint64_t HELPER(paired_cmpxchg64_be)(CPUARMState *env, uint64_t addr, >> /* ??? Enforce alignment. */ >> uint64_t *haddr = g2h(addr); >> >> - helper_retaddr = ra; >> + set_helper_retaddr(ra); >> o1 = ldq_be_p(haddr + 0); >> o0 = ldq_be_p(haddr + 1); >> oldv = int128_make128(o0, o1); >> @@ -634,7 +634,7 @@ uint64_t HELPER(paired_cmpxchg64_be)(CPUARMState *env, uint64_t addr, >> stq_be_p(haddr + 0, int128_gethi(newv)); >> stq_be_p(haddr + 1, int128_getlo(newv)); >> } >> - helper_retaddr = 0; >> + clear_helper_retaddr(); >> #else >> int mem_idx = cpu_mmu_index(env, false); >> TCGMemOpIdx oi0 = make_memop_idx(MO_BEQ | MO_ALIGN_16, mem_idx); >> diff --git a/target/arm/sve_helper.c b/target/arm/sve_helper.c >> index fd434c66ea..fc0c1755d2 100644 >> --- a/target/arm/sve_helper.c >> +++ b/target/arm/sve_helper.c >> @@ -4125,12 +4125,11 @@ static intptr_t max_for_page(target_ulong base, intptr_t mem_off, >> return MIN(split, mem_max - mem_off) + mem_off; >> } >> >> -static inline void set_helper_retaddr(uintptr_t ra) >> -{ >> -#ifdef CONFIG_USER_ONLY >> - helper_retaddr = ra; >> +#ifndef CONFIG_USER_ONLY >> +/* These are normally defined only for CONFIG_USER_ONLY in */ >> +static inline void set_helper_retaddr(uintptr_t ra) { } >> +static inline void clear_helper_retaddr(void) { } > > Why aren't these stubs in the #else leg of cpu_ldst.h? I'm not sure it makes sense to spread these around generically, since they are no-ops which require the extra help of the "host_fn" pointers within that file. In particular, the softmmu host_fn continues to use ra, while the linux-user host_fn does not. Indeed, the whole point of sve_helper.c using set_helper_retaddr is to hoist the setting of helper_retaddr that would be done for each occurrence of cpu_ld_data_ra() et al. r~