| Message ID | 20190926190846.3072-2-msys.mizuma@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64/sve: Fix wrong free for task->thread.sve_state | expand |
(+ Dave) Hi, Thank you for the patch. On 26/09/2019 20:08, Masayoshi Mizuma wrote: > From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> > > The system which has SVE feature crashed because of > the memory pointed by task->thread.sve_state was destroyed > by someone. > > That is because sve_state is freed while the forking the > child process. The child process has the pointer of sve_state > which is same as the parent's because the child's task_struct > is copied from the parent's one. If the copy_process() > fails as an error on somewhere, for example, copy_creds(), > then the sve_state is freed even if the parent is alive. > The flow is as follows. > > copy_process > p = dup_task_struct > => arch_dup_task_struct > *dst = *src; // copy the entire region. > : > retval = copy_creds > if (retval < 0) > goto bad_fork_free; > : > bad_fork_free: > ... > delayed_free_task(p); > => free_task > => arch_release_task_struct > => fpsimd_release_task > => __sve_free > => kfree(task->thread.sve_state); > // free the parent's sve_state The flow makes sense to me and I agree you would end up to free the parent's state. > > Add a flag in task->thread which shows the fork is in progress. > If the fork is in progress, that means the child has the pointer > to the parent's sve_state, doesn't free the sve_state. I haven't fully investigate it yet but I was wondering if we could just clear task->thread.sve_state for the child in arch_dup_task_struct(). I saw the comment on top of function mentioning potential issue to do it there. I understand that you may not be able to clear TIF_SVE in the function, but I don't understand why clearing just task->thread.sve_state would be an issue. The only risk I can see is TIF_SVE may be set with task->thread.sve_state to be NULL. But this is a new task, so I don't think there are risk here to have it unsync. Dave? > > Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> > Reported-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> > --- > arch/arm64/include/asm/processor.h | 1 + > arch/arm64/kernel/fpsimd.c | 6 ++++-- > arch/arm64/kernel/process.c | 2 ++ > 3 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 5623685c7d13..3ca3e350145a 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -143,6 +143,7 @@ struct thread_struct { > unsigned long fault_address; /* fault info */ > unsigned long fault_code; /* ESR_EL1 value */ > struct debug_info debug; /* debugging */ > + unsigned int fork_in_progress; > #ifdef CONFIG_ARM64_PTR_AUTH > struct ptrauth_keys keys_user; > #endif > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index 37d3912cfe06..8641db4cb062 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -202,8 +202,10 @@ static bool have_cpu_fpsimd_context(void) > */ > static void __sve_free(struct task_struct *task) > { > - kfree(task->thread.sve_state); > - task->thread.sve_state = NULL; > + if (!task->thread.fork_in_progress) { > + kfree(task->thread.sve_state); > + task->thread.sve_state = NULL; > + } > } > > static void sve_free(struct task_struct *task) > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index a47462def04b..8ac0ee4e5f76 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -347,6 +347,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > if (current->mm) > fpsimd_preserve_current_state(); > *dst = *src; > + dst->thread.fork_in_progress = 1; > > return 0; > } > @@ -365,6 +366,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > * and disable discard SVE state for p: > */ > clear_tsk_thread_flag(p, TIF_SVE); > + p->thread.fork_in_progress = 0; > p->thread.sve_state = NULL; > > /* > Cheers,
On Thu, Sep 26, 2019 at 03:08:46PM -0400, Masayoshi Mizuma wrote: > From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> > > The system which has SVE feature crashed because of > the memory pointed by task->thread.sve_state was destroyed > by someone. > > That is because sve_state is freed while the forking the > child process. The child process has the pointer of sve_state > which is same as the parent's because the child's task_struct > is copied from the parent's one. If the copy_process() > fails as an error on somewhere, for example, copy_creds(), > then the sve_state is freed even if the parent is alive. > The flow is as follows. > > copy_process > p = dup_task_struct > => arch_dup_task_struct > *dst = *src; // copy the entire region. > : > retval = copy_creds > if (retval < 0) > goto bad_fork_free; > : > bad_fork_free: > ... > delayed_free_task(p); > => free_task > => arch_release_task_struct > => fpsimd_release_task > => __sve_free > => kfree(task->thread.sve_state); > // free the parent's sve_state > > Add a flag in task->thread which shows the fork is in progress. > If the fork is in progress, that means the child has the pointer > to the parent's sve_state, doesn't free the sve_state. > > Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> > Reported-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> > --- > arch/arm64/include/asm/processor.h | 1 + > arch/arm64/kernel/fpsimd.c | 6 ++++-- > arch/arm64/kernel/process.c | 2 ++ > 3 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 5623685c7d13..3ca3e350145a 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -143,6 +143,7 @@ struct thread_struct { > unsigned long fault_address; /* fault info */ > unsigned long fault_code; /* ESR_EL1 value */ > struct debug_info debug; /* debugging */ > + unsigned int fork_in_progress; > #ifdef CONFIG_ARM64_PTR_AUTH > struct ptrauth_keys keys_user; > #endif > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index 37d3912cfe06..8641db4cb062 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -202,8 +202,10 @@ static bool have_cpu_fpsimd_context(void) > */ > static void __sve_free(struct task_struct *task) > { > - kfree(task->thread.sve_state); > - task->thread.sve_state = NULL; > + if (!task->thread.fork_in_progress) { > + kfree(task->thread.sve_state); > + task->thread.sve_state = NULL; > + } > } > > static void sve_free(struct task_struct *task) > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index a47462def04b..8ac0ee4e5f76 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -347,6 +347,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > if (current->mm) > fpsimd_preserve_current_state(); > *dst = *src; > + dst->thread.fork_in_progress = 1; > > return 0; > } > @@ -365,6 +366,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > * and disable discard SVE state for p: > */ > clear_tsk_thread_flag(p, TIF_SVE); > + p->thread.fork_in_progress = 0; > p->thread.sve_state = NULL; There's definitely a problem here, but a simpler fix is probably to NULL sve_state and clear TIF_SVE for dst at the same time. Once upon a time, I had to cope with the thread_flags not being copied as part of task_struct here, which is one reason why the code is the (broken) way it is, but this is ancient history... Commit c02433dd6de3 ("arm64: split thread_info from task stack") was merged in v4.10 and predates SVE support anyway. So can just do the following (untested) and delete the confusing comments? Cheers ---Dave --8<-- diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index f674f28..6937f59 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -323,22 +323,16 @@ void arch_release_task_struct(struct task_struct *tsk) fpsimd_release_task(tsk); } -/* - * src and dst may temporarily have aliased sve_state after task_struct - * is copied. We cannot fix this properly here, because src may have - * live SVE state and dst's thread_info may not exist yet, so tweaking - * either src's or dst's TIF_SVE is not safe. - * - * The unaliasing is done in copy_thread() instead. This works because - * dst is not schedulable or traceable until both of these functions - * have been called. - */ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) { if (current->mm) fpsimd_preserve_current_state(); *dst = *src; + BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK)); + dst->thread.sve_state = NULL; + clear_tsk_thread_flag(dst, TIF_SVE); + return 0; } @@ -352,13 +346,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context)); /* - * Unalias p->thread.sve_state (if any) from the parent task - * and disable discard SVE state for p: - */ - clear_tsk_thread_flag(p, TIF_SVE); - p->thread.sve_state = NULL; - - /* * In case p was allocated the same task_struct pointer as some * other recently-exited task, make sure p is disassociated from * any cpu that may have run that now-exited task recently.
Hi Julien and Dave, Thank you for your comments! Dave's suggestion looks good for me, many thanks! I'll post it as v2. - Masa On Fri, Sep 27, 2019 at 01:52:30PM +0100, Dave Martin wrote: > On Thu, Sep 26, 2019 at 03:08:46PM -0400, Masayoshi Mizuma wrote: > > From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> > > > > The system which has SVE feature crashed because of > > the memory pointed by task->thread.sve_state was destroyed > > by someone. > > > > That is because sve_state is freed while the forking the > > child process. The child process has the pointer of sve_state > > which is same as the parent's because the child's task_struct > > is copied from the parent's one. If the copy_process() > > fails as an error on somewhere, for example, copy_creds(), > > then the sve_state is freed even if the parent is alive. > > The flow is as follows. > > > > copy_process > > p = dup_task_struct > > => arch_dup_task_struct > > *dst = *src; // copy the entire region. > > : > > retval = copy_creds > > if (retval < 0) > > goto bad_fork_free; > > : > > bad_fork_free: > > ... > > delayed_free_task(p); > > => free_task > > => arch_release_task_struct > > => fpsimd_release_task > > => __sve_free > > => kfree(task->thread.sve_state); > > // free the parent's sve_state > > > > Add a flag in task->thread which shows the fork is in progress. > > If the fork is in progress, that means the child has the pointer > > to the parent's sve_state, doesn't free the sve_state. > > > > Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> > > Reported-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> > > --- > > arch/arm64/include/asm/processor.h | 1 + > > arch/arm64/kernel/fpsimd.c | 6 ++++-- > > arch/arm64/kernel/process.c | 2 ++ > > 3 files changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > > index 5623685c7d13..3ca3e350145a 100644 > > --- a/arch/arm64/include/asm/processor.h > > +++ b/arch/arm64/include/asm/processor.h > > @@ -143,6 +143,7 @@ struct thread_struct { > > unsigned long fault_address; /* fault info */ > > unsigned long fault_code; /* ESR_EL1 value */ > > struct debug_info debug; /* debugging */ > > + unsigned int fork_in_progress; > > #ifdef CONFIG_ARM64_PTR_AUTH > > struct ptrauth_keys keys_user; > > #endif > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > > index 37d3912cfe06..8641db4cb062 100644 > > --- a/arch/arm64/kernel/fpsimd.c > > +++ b/arch/arm64/kernel/fpsimd.c > > @@ -202,8 +202,10 @@ static bool have_cpu_fpsimd_context(void) > > */ > > static void __sve_free(struct task_struct *task) > > { > > - kfree(task->thread.sve_state); > > - task->thread.sve_state = NULL; > > + if (!task->thread.fork_in_progress) { > > + kfree(task->thread.sve_state); > > + task->thread.sve_state = NULL; > > + } > > } > > > > static void sve_free(struct task_struct *task) > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > index a47462def04b..8ac0ee4e5f76 100644 > > --- a/arch/arm64/kernel/process.c > > +++ b/arch/arm64/kernel/process.c > > @@ -347,6 +347,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > > if (current->mm) > > fpsimd_preserve_current_state(); > > *dst = *src; > > + dst->thread.fork_in_progress = 1; > > > > return 0; > > } > > @@ -365,6 +366,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > > * and disable discard SVE state for p: > > */ > > clear_tsk_thread_flag(p, TIF_SVE); > > + p->thread.fork_in_progress = 0; > > p->thread.sve_state = NULL; > > There's definitely a problem here, but a simpler fix is probably to > NULL sve_state and clear TIF_SVE for dst at the same time. > > Once upon a time, I had to cope with the thread_flags not being copied > as part of task_struct here, which is one reason why the code is the > (broken) way it is, but this is ancient history... > > Commit c02433dd6de3 ("arm64: split thread_info from task stack") was > merged in v4.10 and predates SVE support anyway. > > > So can just do the following (untested) and delete the confusing > comments? > > Cheers > ---Dave > > --8<-- > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index f674f28..6937f59 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -323,22 +323,16 @@ void arch_release_task_struct(struct task_struct *tsk) > fpsimd_release_task(tsk); > } > > -/* > - * src and dst may temporarily have aliased sve_state after task_struct > - * is copied. We cannot fix this properly here, because src may have > - * live SVE state and dst's thread_info may not exist yet, so tweaking > - * either src's or dst's TIF_SVE is not safe. > - * > - * The unaliasing is done in copy_thread() instead. This works because > - * dst is not schedulable or traceable until both of these functions > - * have been called. > - */ > int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > { > if (current->mm) > fpsimd_preserve_current_state(); > *dst = *src; > > + BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK)); > + dst->thread.sve_state = NULL; > + clear_tsk_thread_flag(dst, TIF_SVE); > + > return 0; > } > > @@ -352,13 +346,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context)); > > /* > - * Unalias p->thread.sve_state (if any) from the parent task > - * and disable discard SVE state for p: > - */ > - clear_tsk_thread_flag(p, TIF_SVE); > - p->thread.sve_state = NULL; > - > - /* > * In case p was allocated the same task_struct pointer as some > * other recently-exited task, make sure p is disassociated from > * any cpu that may have run that now-exited task recently.
On Fri, Sep 27, 2019 at 10:38:02AM -0400, Masayoshi Mizuma wrote: > Hi Julien and Dave, > > Thank you for your comments! > Dave's suggestion looks good for me, many thanks! > I'll post it as v2. Please add Fixes and Cc: stable tags as appropriate. (I'm happy not to push this patch myself, but I would expect to see a Suggested-by tag...) See Documentation/process/submitting-patches.rst, Documentation/process/stable-kernel-rules.txt if unsure. [...] Cheers ---Dave
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 5623685c7d13..3ca3e350145a 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -143,6 +143,7 @@ struct thread_struct { unsigned long fault_address; /* fault info */ unsigned long fault_code; /* ESR_EL1 value */ struct debug_info debug; /* debugging */ + unsigned int fork_in_progress; #ifdef CONFIG_ARM64_PTR_AUTH struct ptrauth_keys keys_user; #endif diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 37d3912cfe06..8641db4cb062 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -202,8 +202,10 @@ static bool have_cpu_fpsimd_context(void) */ static void __sve_free(struct task_struct *task) { - kfree(task->thread.sve_state); - task->thread.sve_state = NULL; + if (!task->thread.fork_in_progress) { + kfree(task->thread.sve_state); + task->thread.sve_state = NULL; + } } static void sve_free(struct task_struct *task) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index a47462def04b..8ac0ee4e5f76 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -347,6 +347,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) if (current->mm) fpsimd_preserve_current_state(); *dst = *src; + dst->thread.fork_in_progress = 1; return 0; } @@ -365,6 +366,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, * and disable discard SVE state for p: */ clear_tsk_thread_flag(p, TIF_SVE); + p->thread.fork_in_progress = 0; p->thread.sve_state = NULL; /*