| Message ID | 20230108163905.59601-2-cota@braap.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | tsan fixes | expand |
On 1/8/23 08:39, Emilio Cota wrote: > Fixes the appended use-after-free. The root cause is that > during tb invalidation we use CPU_FOREACH, and therefore > to safely free a vCPU we must wait for an RCU grace period > to elapse. > > $ x86_64-linux-user/qemu-x86_64 tests/tcg/x86_64-linux-user/munmap-pthread > ================================================================= > ==1800604==ERROR: AddressSanitizer: heap-use-after-free on address 0x62d0005f7418 at pc 0x5593da6704eb bp 0x7f4961a7ac70 sp 0x7f4961a7ac60 > READ of size 8 at 0x62d0005f7418 thread T2 > #0 0x5593da6704ea in tb_jmp_cache_inval_tb ../accel/tcg/tb-maint.c:244 > #1 0x5593da6704ea in do_tb_phys_invalidate ../accel/tcg/tb-maint.c:290 > #2 0x5593da670631 in tb_phys_invalidate__locked ../accel/tcg/tb-maint.c:306 > #3 0x5593da670631 in tb_invalidate_phys_page_range__locked ../accel/tcg/tb-maint.c:542 > #4 0x5593da67106d in tb_invalidate_phys_range ../accel/tcg/tb-maint.c:614 > #5 0x5593da6a64d4 in target_munmap ../linux-user/mmap.c:766 > #6 0x5593da6dba05 in do_syscall1 ../linux-user/syscall.c:10105 > #7 0x5593da6f564c in do_syscall ../linux-user/syscall.c:13329 > #8 0x5593da49e80c in cpu_loop ../linux-user/x86_64/../i386/cpu_loop.c:233 > #9 0x5593da6be28c in clone_func ../linux-user/syscall.c:6633 > #10 0x7f496231cb42 in start_thread nptl/pthread_create.c:442 > #11 0x7f49623ae9ff (/lib/x86_64-linux-gnu/libc.so.6+0x1269ff) > > 0x62d0005f7418 is located 28696 bytes inside of 32768-byte region [0x62d0005f0400,0x62d0005f8400) > freed by thread T148 here: > #0 0x7f49627b6460 in __interceptor_free ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:52 > #1 0x5593da5ac057 in cpu_exec_unrealizefn ../cpu.c:180 > #2 0x5593da81f851 (/home/cota/src/qemu/build/qemu-x86_64+0x484851) > > Signed-off-by: Emilio Cota <cota@braap.org> > --- > accel/tcg/cpu-exec.c | 1 - > cpu.c | 7 +++++++ > include/hw/core/cpu.h | 3 +++ > 3 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c > index 356fe348de..ca95d21528 100644 > --- a/accel/tcg/cpu-exec.c > +++ b/accel/tcg/cpu-exec.c > @@ -1070,7 +1070,6 @@ void tcg_exec_unrealizefn(CPUState *cpu) > #endif /* !CONFIG_USER_ONLY */ > > tlb_destroy(cpu); > - g_free(cpu->tb_jmp_cache); Can you simply use g_free_rcu here? > } > > #ifndef CONFIG_USER_ONLY > diff --git a/cpu.c b/cpu.c > index 4a7d865427..564200559f 100644 > --- a/cpu.c > +++ b/cpu.c > @@ -164,6 +164,12 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp) > #endif /* CONFIG_USER_ONLY */ > } > > +static void cpu_free_rcu(CPUState *cpu) > +{ > + /* .tb_jmp_cache is NULL except under TCG */ > + g_free(cpu->tb_jmp_cache); > +} > + > void cpu_exec_unrealizefn(CPUState *cpu) > { > #ifndef CONFIG_USER_ONLY > @@ -181,6 +187,7 @@ void cpu_exec_unrealizefn(CPUState *cpu) > } > > cpu_list_remove(cpu); > + call_rcu(cpu, cpu_free_rcu, rcu); Certainly this seems wrong, exposing tb_jmp_cache beyond tcg. r~
On Sun, Jan 08, 2023 at 11:19:53 -0800, Richard Henderson wrote: > On 1/8/23 08:39, Emilio Cota wrote: (snip) > > diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c > > index 356fe348de..ca95d21528 100644 > > --- a/accel/tcg/cpu-exec.c > > +++ b/accel/tcg/cpu-exec.c > > @@ -1070,7 +1070,6 @@ void tcg_exec_unrealizefn(CPUState *cpu) > > #endif /* !CONFIG_USER_ONLY */ > > tlb_destroy(cpu); > > - g_free(cpu->tb_jmp_cache); > > Can you simply use g_free_rcu here? Yes, although we must have removed the CPU from the RCU list before doing so. > > diff --git a/cpu.c b/cpu.c > > index 4a7d865427..564200559f 100644 > > --- a/cpu.c > > +++ b/cpu.c > > @@ -164,6 +164,12 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp) > > #endif /* CONFIG_USER_ONLY */ > > } > > +static void cpu_free_rcu(CPUState *cpu) > > +{ > > + /* .tb_jmp_cache is NULL except under TCG */ > > + g_free(cpu->tb_jmp_cache); > > +} > > + > > void cpu_exec_unrealizefn(CPUState *cpu) > > { > > #ifndef CONFIG_USER_ONLY > > @@ -181,6 +187,7 @@ void cpu_exec_unrealizefn(CPUState *cpu) > > } > > cpu_list_remove(cpu); > > + call_rcu(cpu, cpu_free_rcu, rcu); > > Certainly this seems wrong, exposing tb_jmp_cache beyond tcg. I've changed this in v2 to call tcg_exec_unrealizefn after cpu_list_remove. An alternative would be to call the whole cpu_exec_unrealizefn after an RCU grace period, but I think that might be more trouble than it's worth. Thanks, Emilio
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c index 356fe348de..ca95d21528 100644 --- a/accel/tcg/cpu-exec.c +++ b/accel/tcg/cpu-exec.c @@ -1070,7 +1070,6 @@ void tcg_exec_unrealizefn(CPUState *cpu) #endif /* !CONFIG_USER_ONLY */ tlb_destroy(cpu); - g_free(cpu->tb_jmp_cache); } #ifndef CONFIG_USER_ONLY diff --git a/cpu.c b/cpu.c index 4a7d865427..564200559f 100644 --- a/cpu.c +++ b/cpu.c @@ -164,6 +164,12 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp) #endif /* CONFIG_USER_ONLY */ } +static void cpu_free_rcu(CPUState *cpu) +{ + /* .tb_jmp_cache is NULL except under TCG */ + g_free(cpu->tb_jmp_cache); +} + void cpu_exec_unrealizefn(CPUState *cpu) { #ifndef CONFIG_USER_ONLY @@ -181,6 +187,7 @@ void cpu_exec_unrealizefn(CPUState *cpu) } cpu_list_remove(cpu); + call_rcu(cpu, cpu_free_rcu, rcu); } /* diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index 8830546121..9fefad5656 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -266,6 +266,7 @@ struct qemu_work_item; /** * CPUState: + * @rcu: Used for safe deferred memory reclamation. * @cpu_index: CPU index (informative). * @cluster_index: Identifies which cluster this CPU is in. * For boards which don't define clusters or for "loose" CPUs not assigned @@ -321,6 +322,8 @@ struct qemu_work_item; * State of one CPU core or thread. */ struct CPUState { + struct rcu_head rcu; + /*< private >*/ DeviceState parent_obj; /* cache to avoid expensive CPU_GET_CLASS */
Fixes the appended use-after-free. The root cause is that during tb invalidation we use CPU_FOREACH, and therefore to safely free a vCPU we must wait for an RCU grace period to elapse. $ x86_64-linux-user/qemu-x86_64 tests/tcg/x86_64-linux-user/munmap-pthread ================================================================= ==1800604==ERROR: AddressSanitizer: heap-use-after-free on address 0x62d0005f7418 at pc 0x5593da6704eb bp 0x7f4961a7ac70 sp 0x7f4961a7ac60 READ of size 8 at 0x62d0005f7418 thread T2 #0 0x5593da6704ea in tb_jmp_cache_inval_tb ../accel/tcg/tb-maint.c:244 #1 0x5593da6704ea in do_tb_phys_invalidate ../accel/tcg/tb-maint.c:290 #2 0x5593da670631 in tb_phys_invalidate__locked ../accel/tcg/tb-maint.c:306 #3 0x5593da670631 in tb_invalidate_phys_page_range__locked ../accel/tcg/tb-maint.c:542 #4 0x5593da67106d in tb_invalidate_phys_range ../accel/tcg/tb-maint.c:614 #5 0x5593da6a64d4 in target_munmap ../linux-user/mmap.c:766 #6 0x5593da6dba05 in do_syscall1 ../linux-user/syscall.c:10105 #7 0x5593da6f564c in do_syscall ../linux-user/syscall.c:13329 #8 0x5593da49e80c in cpu_loop ../linux-user/x86_64/../i386/cpu_loop.c:233 #9 0x5593da6be28c in clone_func ../linux-user/syscall.c:6633 #10 0x7f496231cb42 in start_thread nptl/pthread_create.c:442 #11 0x7f49623ae9ff (/lib/x86_64-linux-gnu/libc.so.6+0x1269ff) 0x62d0005f7418 is located 28696 bytes inside of 32768-byte region [0x62d0005f0400,0x62d0005f8400) freed by thread T148 here: #0 0x7f49627b6460 in __interceptor_free ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:52 #1 0x5593da5ac057 in cpu_exec_unrealizefn ../cpu.c:180 #2 0x5593da81f851 (/home/cota/src/qemu/build/qemu-x86_64+0x484851) Signed-off-by: Emilio Cota <cota@braap.org> --- accel/tcg/cpu-exec.c | 1 - cpu.c | 7 +++++++ include/hw/core/cpu.h | 3 +++ 3 files changed, 10 insertions(+), 1 deletion(-)