| Message ID | 1449195519-17901-3-git-send-email-huawei.libin@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 4 Dec 2015 10:18:39 +0800 Li Bin <huawei.libin@huawei.com> wrote: > There is no need to worry about module text disappearing case, > because that ftrace has a module notifier that is called when > a module is being unloaded and before the text goes away, and this > code grabs the ftrace_lock mutex and removes the module functions > from the ftrace list, such that it will no longer do any > modifications to that module's text. > The update to make functions be traced or not is done under the > ftrace_lock mutex as well. > > Signed-off-by: Li Bin <huawei.libin@huawei.com> > --- > arch/arm64/kernel/ftrace.c | 5 +---- > 1 files changed, 1 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index 9669b33..ee91c0c 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -29,12 +29,9 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, > > /* > * Note: > - * Due to modules and __init, code can disappear and change, > + * Due to __init, code can disappear and change, Init code should not be modified either because it is black listed in recordmcount.c. I say just change the comment to be something like: We are paranoid about modifying text, as if a bug were to happen, it could cause us to read or write to someplace that could cause harm. Carefully read and modify the code with aarch64_insn_*() which uses probe_kernel_*(), and make sure what we read is what we expected it to be before modifying it. -- Steve > * we need to protect against faulting as well as code changing. > * We do this by aarch64_insn_*() which use the probe_kernel_*(). > - * > - * No lock is held here because all the modifications are run > - * through stop_machine(). > */ > if (validate) { > if (aarch64_insn_read((void *)pc, &replaced))
on 2015/12/4 10:50, Steven Rostedt wrote: > On Fri, 4 Dec 2015 10:18:39 +0800 > Li Bin <huawei.libin@huawei.com> wrote: > >> There is no need to worry about module text disappearing case, >> because that ftrace has a module notifier that is called when >> a module is being unloaded and before the text goes away, and this >> code grabs the ftrace_lock mutex and removes the module functions >> from the ftrace list, such that it will no longer do any >> modifications to that module's text. >> The update to make functions be traced or not is done under the >> ftrace_lock mutex as well. >> >> Signed-off-by: Li Bin <huawei.libin@huawei.com> >> --- >> arch/arm64/kernel/ftrace.c | 5 +---- >> 1 files changed, 1 insertions(+), 4 deletions(-) >> >> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c >> index 9669b33..ee91c0c 100644 >> --- a/arch/arm64/kernel/ftrace.c >> +++ b/arch/arm64/kernel/ftrace.c >> @@ -29,12 +29,9 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, >> >> /* >> * Note: >> - * Due to modules and __init, code can disappear and change, >> + * Due to __init, code can disappear and change, > Init code should not be modified either because it is black listed in > recordmcount.c. > > I say just change the comment to be something like: > > We are paranoid about modifying text, as if a bug were to happen, it > could cause us to read or write to someplace that could cause harm. > Carefully read and modify the code with aarch64_insn_*() which uses > probe_kernel_*(), and make sure what we read is what we expected it to > be before modifying it. Ok, I will modify it. Thanks, Li Bin > -- Steve > > >> * we need to protect against faulting as well as code changing. >> * We do this by aarch64_insn_*() which use the probe_kernel_*(). >> - * >> - * No lock is held here because all the modifications are run >> - * through stop_machine(). >> */ >> if (validate) { >> if (aarch64_insn_read((void *)pc, &replaced)) > > . >
I will also update the comment for the other arch that using the similar description, such as ia64/metag/powerpc/sh/x86. Thanks, Li Bin on 2015/12/4 10:50, Steven Rostedt wrote: > On Fri, 4 Dec 2015 10:18:39 +0800 > Li Bin <huawei.libin@huawei.com> wrote: > >> There is no need to worry about module text disappearing case, >> because that ftrace has a module notifier that is called when >> a module is being unloaded and before the text goes away, and this >> code grabs the ftrace_lock mutex and removes the module functions >> from the ftrace list, such that it will no longer do any >> modifications to that module's text. >> The update to make functions be traced or not is done under the >> ftrace_lock mutex as well. >> >> Signed-off-by: Li Bin <huawei.libin@huawei.com> >> --- >> arch/arm64/kernel/ftrace.c | 5 +---- >> 1 files changed, 1 insertions(+), 4 deletions(-) >> >> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c >> index 9669b33..ee91c0c 100644 >> --- a/arch/arm64/kernel/ftrace.c >> +++ b/arch/arm64/kernel/ftrace.c >> @@ -29,12 +29,9 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, >> >> /* >> * Note: >> - * Due to modules and __init, code can disappear and change, >> + * Due to __init, code can disappear and change, > Init code should not be modified either because it is black listed in > recordmcount.c. > > I say just change the comment to be something like: > > We are paranoid about modifying text, as if a bug were to happen, it > could cause us to read or write to someplace that could cause harm. > Carefully read and modify the code with aarch64_insn_*() which uses > probe_kernel_*(), and make sure what we read is what we expected it to > be before modifying it. > > -- Steve > > >> * we need to protect against faulting as well as code changing. >> * We do this by aarch64_insn_*() which use the probe_kernel_*(). >> - * >> - * No lock is held here because all the modifications are run >> - * through stop_machine(). >> */ >> if (validate) { >> if (aarch64_insn_read((void *)pc, &replaced)) > > . >
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index 9669b33..ee91c0c 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -29,12 +29,9 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, /* * Note: - * Due to modules and __init, code can disappear and change, + * Due to __init, code can disappear and change, * we need to protect against faulting as well as code changing. * We do this by aarch64_insn_*() which use the probe_kernel_*(). - * - * No lock is held here because all the modifications are run - * through stop_machine(). */ if (validate) { if (aarch64_insn_read((void *)pc, &replaced))
There is no need to worry about module text disappearing case, because that ftrace has a module notifier that is called when a module is being unloaded and before the text goes away, and this code grabs the ftrace_lock mutex and removes the module functions from the ftrace list, such that it will no longer do any modifications to that module's text. The update to make functions be traced or not is done under the ftrace_lock mutex as well. Signed-off-by: Li Bin <huawei.libin@huawei.com> --- arch/arm64/kernel/ftrace.c | 5 +---- 1 files changed, 1 insertions(+), 4 deletions(-)