* [PATCH] kexec: should use uchunk for user buffer increasing @ 2024-01-30 10:18 yang.zhang 2024-02-04 7:38 ` Baoquan He 0 siblings, 1 reply; 7+ messages in thread From: yang.zhang @ 2024-01-30 10:18 UTC (permalink / raw) To: ebiederm; +Cc: kexec, linux-kernel, yang.zhang From: "yang.zhang" <yang.zhang@hexintek.com> Because of alignment requirement in kexec-tools, there is no problem for user buffer increasing when loading segments. But when coping, the step is uchunk, so we should use uchunk not mchunk. Signed-off-by: yang.zhang <yang.zhang@hexintek.com> --- kernel/kexec_core.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index d08fc7b5db97..2b8354313c85 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -813,9 +813,9 @@ static int kimage_load_normal_segment(struct kimage *image, ubytes -= uchunk; maddr += mchunk; if (image->file_mode) - kbuf += mchunk; + kbuf += uchunk; else - buf += mchunk; + buf += uchunk; mbytes -= mchunk; cond_resched(); @@ -881,9 +881,9 @@ static int kimage_load_crash_segment(struct kimage *image, ubytes -= uchunk; maddr += mchunk; if (image->file_mode) - kbuf += mchunk; + kbuf += uchunk; else - buf += mchunk; + buf += uchunk; mbytes -= mchunk; cond_resched(); -- 2.34.1 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] kexec: should use uchunk for user buffer increasing 2024-01-30 10:18 [PATCH] kexec: should use uchunk for user buffer increasing yang.zhang @ 2024-02-04 7:38 ` Baoquan He 2024-02-05 12:27 ` Eric W. Biederman 0 siblings, 1 reply; 7+ messages in thread From: Baoquan He @ 2024-02-04 7:38 UTC (permalink / raw) To: yang.zhang; +Cc: ebiederm, kexec, linux-kernel, yang.zhang On 01/30/24 at 06:18pm, yang.zhang wrote: > From: "yang.zhang" <yang.zhang@hexintek.com> > > Because of alignment requirement in kexec-tools, there is > no problem for user buffer increasing when loading segments. > But when coping, the step is uchunk, so we should use uchunk > not mchunk. In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes is exhausted, while there's still remaining mbytes, then uchunk is 0, there's still mchunk stepping forward. If I understand it correctly, this is a good catch. Not sure if Eric has comment on this to confirm. static int kimage_load_normal_segment(struct kimage *image, struct kexec_segment *segment) { ...... ptr += maddr & ~PAGE_MASK; mchunk = min_t(size_t, mbytes, PAGE_SIZE - (maddr & ~PAGE_MASK)); uchunk = min(ubytes, mchunk); ......} > > Signed-off-by: yang.zhang <yang.zhang@hexintek.com> > --- > kernel/kexec_core.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index d08fc7b5db97..2b8354313c85 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -813,9 +813,9 @@ static int kimage_load_normal_segment(struct kimage *image, > ubytes -= uchunk; > maddr += mchunk; > if (image->file_mode) > - kbuf += mchunk; > + kbuf += uchunk; > else > - buf += mchunk; > + buf += uchunk; > mbytes -= mchunk; > > cond_resched(); > @@ -881,9 +881,9 @@ static int kimage_load_crash_segment(struct kimage *image, > ubytes -= uchunk; > maddr += mchunk; > if (image->file_mode) > - kbuf += mchunk; > + kbuf += uchunk; > else > - buf += mchunk; > + buf += uchunk; > mbytes -= mchunk; > > cond_resched(); > -- > 2.34.1 > > > _______________________________________________ > kexec mailing list > kexec@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] kexec: should use uchunk for user buffer increasing 2024-02-04 7:38 ` Baoquan He @ 2024-02-05 12:27 ` Eric W. Biederman 2024-02-05 12:59 ` Baoquan He 2024-02-19 2:00 ` yang.zhang 0 siblings, 2 replies; 7+ messages in thread From: Eric W. Biederman @ 2024-02-05 12:27 UTC (permalink / raw) To: Baoquan He; +Cc: yang.zhang, kexec, linux-kernel, yang.zhang Baoquan He <bhe@redhat.com> writes: > On 01/30/24 at 06:18pm, yang.zhang wrote: >> From: "yang.zhang" <yang.zhang@hexintek.com> >> >> Because of alignment requirement in kexec-tools, there is >> no problem for user buffer increasing when loading segments. >> But when coping, the step is uchunk, so we should use uchunk >> not mchunk. > > In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes > is exhausted, while there's still remaining mbytes, then uchunk is 0, > there's still mchunk stepping forward. If I understand it correctly, > this is a good catch. Not sure if Eric has comment on this to confirm. As far as I can read the code the proposed change is a noop. I agree it is more correct to not advance the pointers we read from, but since we never read from them after that point it does not matter. > > static int kimage_load_normal_segment(struct kimage *image, > struct kexec_segment *segment) > { > ...... > > ptr += maddr & ~PAGE_MASK; > mchunk = min_t(size_t, mbytes, > PAGE_SIZE - (maddr & ~PAGE_MASK)); > uchunk = min(ubytes, mchunk); > ......} If we are going to improve the code for clarity. We probably want to do something like: diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index d08fc7b5db97..1a8b8ce6bf15 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image, PAGE_SIZE - (maddr & ~PAGE_MASK)); uchunk = min(ubytes, mchunk); - /* For file based kexec, source pages are in kernel memory */ - if (image->file_mode) - memcpy(ptr, kbuf, uchunk); - else - result = copy_from_user(ptr, buf, uchunk); + if (uchunk) { + /* For file based kexec, source pages are in kernel memory */ + if (image->file_mode) + memcpy(ptr, kbuf, uchunk); + else + result = copy_from_user(ptr, buf, uchunk); + ubytes -= uchunk; + if (image->file_mode) + kbuf += uchunk; + else + buf += uchunk; + } kunmap_local(ptr); if (result) { result = -EFAULT; goto out; } - ubytes -= uchunk; maddr += mchunk; - if (image->file_mode) - kbuf += mchunk; - else - buf += mchunk; mbytes -= mchunk; cond_resched(); And make it exceedingly clear that all of the copying and the rest only happens before uchunk goes to zero. Otherwise we are relying on a lot of operations becoming noops when uchunk goes to zero. Eric ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] kexec: should use uchunk for user buffer increasing 2024-02-05 12:27 ` Eric W. Biederman @ 2024-02-05 12:59 ` Baoquan He 2024-02-19 2:00 ` yang.zhang 1 sibling, 0 replies; 7+ messages in thread From: Baoquan He @ 2024-02-05 12:59 UTC (permalink / raw) To: Eric W. Biederman; +Cc: yang.zhang, kexec, linux-kernel, yang.zhang On 02/05/24 at 06:27am, Eric W. Biederman wrote: > Baoquan He <bhe@redhat.com> writes: > > > On 01/30/24 at 06:18pm, yang.zhang wrote: > >> From: "yang.zhang" <yang.zhang@hexintek.com> > >> > >> Because of alignment requirement in kexec-tools, there is > >> no problem for user buffer increasing when loading segments. > >> But when coping, the step is uchunk, so we should use uchunk > >> not mchunk. > > > > In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes > > is exhausted, while there's still remaining mbytes, then uchunk is 0, > > there's still mchunk stepping forward. If I understand it correctly, > > this is a good catch. Not sure if Eric has comment on this to confirm. > > As far as I can read the code the proposed change is a noop. > > I agree it is more correct to not advance the pointers we read from, > but since we never read from them after that point it does not > matter. > > > > > static int kimage_load_normal_segment(struct kimage *image, > > struct kexec_segment *segment) > > { > > ...... > > > > ptr += maddr & ~PAGE_MASK; > > mchunk = min_t(size_t, mbytes, > > PAGE_SIZE - (maddr & ~PAGE_MASK)); > > uchunk = min(ubytes, mchunk); > > ......} > > If we are going to improve the code for clarity. We probably > want to do something like: > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index d08fc7b5db97..1a8b8ce6bf15 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image, > PAGE_SIZE - (maddr & ~PAGE_MASK)); > uchunk = min(ubytes, mchunk); > > - /* For file based kexec, source pages are in kernel memory */ > - if (image->file_mode) > - memcpy(ptr, kbuf, uchunk); > - else > - result = copy_from_user(ptr, buf, uchunk); > + if (uchunk) { > + /* For file based kexec, source pages are in kernel memory */ > + if (image->file_mode) > + memcpy(ptr, kbuf, uchunk); > + else > + result = copy_from_user(ptr, buf, uchunk); > + ubytes -= uchunk; > + if (image->file_mode) > + kbuf += uchunk; > + else > + buf += uchunk; > + } > kunmap_local(ptr); > if (result) { > result = -EFAULT; > goto out; > } > - ubytes -= uchunk; > maddr += mchunk; > - if (image->file_mode) > - kbuf += mchunk; > - else > - buf += mchunk; > mbytes -= mchunk; > > cond_resched(); > > And make it exceedingly clear that all of the copying and the rest > only happens before uchunk goes to zero. Otherwise we are relying > on a lot of operations becoming noops when uchunk goes to zero. ACK. This makes the code logic much clearer, thanks. ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re:Re: [PATCH] kexec: should use uchunk for user buffer increasing 2024-02-05 12:27 ` Eric W. Biederman 2024-02-05 12:59 ` Baoquan He @ 2024-02-19 2:00 ` yang.zhang 2024-02-19 2:38 ` Baoquan He 1 sibling, 1 reply; 7+ messages in thread From: yang.zhang @ 2024-02-19 2:00 UTC (permalink / raw) To: Eric W. Biederman; +Cc: Baoquan He, kexec, linux-kernel, yang.zhang Thanks for your replies. Do you have plans to merge the improving code for clarity, or just keep them unchanged. At 2024-02-05 20:27:33, "Eric W. Biederman" <ebiederm@xmission.com> wrote: >Baoquan He <bhe@redhat.com> writes: > >> On 01/30/24 at 06:18pm, yang.zhang wrote: >>> From: "yang.zhang" <yang.zhang@hexintek.com> >>> >>> Because of alignment requirement in kexec-tools, there is >>> no problem for user buffer increasing when loading segments. >>> But when coping, the step is uchunk, so we should use uchunk >>> not mchunk. >> >> In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes >> is exhausted, while there's still remaining mbytes, then uchunk is 0, >> there's still mchunk stepping forward. If I understand it correctly, >> this is a good catch. Not sure if Eric has comment on this to confirm. > >As far as I can read the code the proposed change is a noop. > >I agree it is more correct to not advance the pointers we read from, >but since we never read from them after that point it does not >matter. > >> >> static int kimage_load_normal_segment(struct kimage *image, >> struct kexec_segment *segment) >> { >> ...... >> >> ptr += maddr & ~PAGE_MASK; >> mchunk = min_t(size_t, mbytes, >> PAGE_SIZE - (maddr & ~PAGE_MASK)); >> uchunk = min(ubytes, mchunk); >> ......} > >If we are going to improve the code for clarity. We probably >want to do something like: > >diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c >index d08fc7b5db97..1a8b8ce6bf15 100644 >--- a/kernel/kexec_core.c >+++ b/kernel/kexec_core.c >@@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image, > PAGE_SIZE - (maddr & ~PAGE_MASK)); > uchunk = min(ubytes, mchunk); > >- /* For file based kexec, source pages are in kernel memory */ >- if (image->file_mode) >- memcpy(ptr, kbuf, uchunk); >- else >- result = copy_from_user(ptr, buf, uchunk); >+ if (uchunk) { >+ /* For file based kexec, source pages are in kernel memory */ >+ if (image->file_mode) >+ memcpy(ptr, kbuf, uchunk); >+ else >+ result = copy_from_user(ptr, buf, uchunk); >+ ubytes -= uchunk; >+ if (image->file_mode) >+ kbuf += uchunk; >+ else >+ buf += uchunk; >+ } > kunmap_local(ptr); > if (result) { > result = -EFAULT; > goto out; > } >- ubytes -= uchunk; > maddr += mchunk; >- if (image->file_mode) >- kbuf += mchunk; >- else >- buf += mchunk; > mbytes -= mchunk; > > cond_resched(); > >And make it exceedingly clear that all of the copying and the rest >only happens before uchunk goes to zero. Otherwise we are relying >on a lot of operations becoming noops when uchunk goes to zero. > >Eric ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] kexec: should use uchunk for user buffer increasing 2024-02-19 2:00 ` yang.zhang @ 2024-02-19 2:38 ` Baoquan He 2024-02-19 9:26 ` yang.zhang 0 siblings, 1 reply; 7+ messages in thread From: Baoquan He @ 2024-02-19 2:38 UTC (permalink / raw) To: yang.zhang; +Cc: Eric W. Biederman, kexec, linux-kernel, yang.zhang, akpm On 02/19/24 at 10:00am, yang.zhang wrote: > > > > Thanks for your replies. > Do you have plans to merge the improving code for clarity, or just keep them unchanged. You need post v2 to change those two places as Eric has demonstrated. Please CC Andrew when you post. > > At 2024-02-05 20:27:33, "Eric W. Biederman" <ebiederm@xmission.com> wrote: > >Baoquan He <bhe@redhat.com> writes: > > > >> On 01/30/24 at 06:18pm, yang.zhang wrote: > >>> From: "yang.zhang" <yang.zhang@hexintek.com> > >>> > >>> Because of alignment requirement in kexec-tools, there is > >>> no problem for user buffer increasing when loading segments. > >>> But when coping, the step is uchunk, so we should use uchunk > >>> not mchunk. > >> > >> In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes > >> is exhausted, while there's still remaining mbytes, then uchunk is 0, > >> there's still mchunk stepping forward. If I understand it correctly, > >> this is a good catch. Not sure if Eric has comment on this to confirm. > > > >As far as I can read the code the proposed change is a noop. > > > >I agree it is more correct to not advance the pointers we read from, > >but since we never read from them after that point it does not > >matter. > > > >> > >> static int kimage_load_normal_segment(struct kimage *image, > >> struct kexec_segment *segment) > >> { > >> ...... > >> > >> ptr += maddr & ~PAGE_MASK; > >> mchunk = min_t(size_t, mbytes, > >> PAGE_SIZE - (maddr & ~PAGE_MASK)); > >> uchunk = min(ubytes, mchunk); > >> ......} > > > >If we are going to improve the code for clarity. We probably > >want to do something like: > > > >diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > >index d08fc7b5db97..1a8b8ce6bf15 100644 > >--- a/kernel/kexec_core.c > >+++ b/kernel/kexec_core.c > >@@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image, > > PAGE_SIZE - (maddr & ~PAGE_MASK)); > > uchunk = min(ubytes, mchunk); > > > >- /* For file based kexec, source pages are in kernel memory */ > >- if (image->file_mode) > >- memcpy(ptr, kbuf, uchunk); > >- else > >- result = copy_from_user(ptr, buf, uchunk); > >+ if (uchunk) { > >+ /* For file based kexec, source pages are in kernel memory */ > >+ if (image->file_mode) > >+ memcpy(ptr, kbuf, uchunk); > >+ else > >+ result = copy_from_user(ptr, buf, uchunk); > >+ ubytes -= uchunk; > >+ if (image->file_mode) > >+ kbuf += uchunk; > >+ else > >+ buf += uchunk; > >+ } > > kunmap_local(ptr); > > if (result) { > > result = -EFAULT; > > goto out; > > } > >- ubytes -= uchunk; > > maddr += mchunk; > >- if (image->file_mode) > >- kbuf += mchunk; > >- else > >- buf += mchunk; > > mbytes -= mchunk; > > > > cond_resched(); > > > >And make it exceedingly clear that all of the copying and the rest > >only happens before uchunk goes to zero. Otherwise we are relying > >on a lot of operations becoming noops when uchunk goes to zero. > > > >Eric ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re:Re: [PATCH] kexec: should use uchunk for user buffer increasing 2024-02-19 2:38 ` Baoquan He @ 2024-02-19 9:26 ` yang.zhang 0 siblings, 0 replies; 7+ messages in thread From: yang.zhang @ 2024-02-19 9:26 UTC (permalink / raw) To: Baoquan He; +Cc: Eric W. Biederman, kexec, linux-kernel, yang.zhang, akpm Thanks, i would post v2 patch. Could you please provide the email address for andrew. At 2024-02-19 10:38:22, "Baoquan He" <bhe@redhat.com> wrote: >On 02/19/24 at 10:00am, yang.zhang wrote: >> >> >> >> Thanks for your replies. >> Do you have plans to merge the improving code for clarity, or just keep them unchanged. > >You need post v2 to change those two places as Eric has demonstrated. >Please CC Andrew when you post. > >> >> At 2024-02-05 20:27:33, "Eric W. Biederman" <ebiederm@xmission.com> wrote: >> >Baoquan He <bhe@redhat.com> writes: >> > >> >> On 01/30/24 at 06:18pm, yang.zhang wrote: >> >>> From: "yang.zhang" <yang.zhang@hexintek.com> >> >>> >> >>> Because of alignment requirement in kexec-tools, there is >> >>> no problem for user buffer increasing when loading segments. >> >>> But when coping, the step is uchunk, so we should use uchunk >> >>> not mchunk. >> >> >> >> In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes >> >> is exhausted, while there's still remaining mbytes, then uchunk is 0, >> >> there's still mchunk stepping forward. If I understand it correctly, >> >> this is a good catch. Not sure if Eric has comment on this to confirm. >> > >> >As far as I can read the code the proposed change is a noop. >> > >> >I agree it is more correct to not advance the pointers we read from, >> >but since we never read from them after that point it does not >> >matter. >> > >> >> >> >> static int kimage_load_normal_segment(struct kimage *image, >> >> struct kexec_segment *segment) >> >> { >> >> ...... >> >> >> >> ptr += maddr & ~PAGE_MASK; >> >> mchunk = min_t(size_t, mbytes, >> >> PAGE_SIZE - (maddr & ~PAGE_MASK)); >> >> uchunk = min(ubytes, mchunk); >> >> ......} >> > >> >If we are going to improve the code for clarity. We probably >> >want to do something like: >> > >> >diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c >> >index d08fc7b5db97..1a8b8ce6bf15 100644 >> >--- a/kernel/kexec_core.c >> >+++ b/kernel/kexec_core.c >> >@@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image, >> > PAGE_SIZE - (maddr & ~PAGE_MASK)); >> > uchunk = min(ubytes, mchunk); >> > >> >- /* For file based kexec, source pages are in kernel memory */ >> >- if (image->file_mode) >> >- memcpy(ptr, kbuf, uchunk); >> >- else >> >- result = copy_from_user(ptr, buf, uchunk); >> >+ if (uchunk) { >> >+ /* For file based kexec, source pages are in kernel memory */ >> >+ if (image->file_mode) >> >+ memcpy(ptr, kbuf, uchunk); >> >+ else >> >+ result = copy_from_user(ptr, buf, uchunk); >> >+ ubytes -= uchunk; >> >+ if (image->file_mode) >> >+ kbuf += uchunk; >> >+ else >> >+ buf += uchunk; >> >+ } >> > kunmap_local(ptr); >> > if (result) { >> > result = -EFAULT; >> > goto out; >> > } >> >- ubytes -= uchunk; >> > maddr += mchunk; >> >- if (image->file_mode) >> >- kbuf += mchunk; >> >- else >> >- buf += mchunk; >> > mbytes -= mchunk; >> > >> > cond_resched(); >> > >> >And make it exceedingly clear that all of the copying and the rest >> >only happens before uchunk goes to zero. Otherwise we are relying >> >on a lot of operations becoming noops when uchunk goes to zero. >> > >> >Eric ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-02-19 9:27 UTC | newest] Thread overview: 7+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2024-01-30 10:18 [PATCH] kexec: should use uchunk for user buffer increasing yang.zhang 2024-02-04 7:38 ` Baoquan He 2024-02-05 12:27 ` Eric W. Biederman 2024-02-05 12:59 ` Baoquan He 2024-02-19 2:00 ` yang.zhang 2024-02-19 2:38 ` Baoquan He 2024-02-19 9:26 ` yang.zhang
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