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Message-ID: <ZMksTC6pewXDgkFe@MiWiFi-R3L-srv>
Date: Wed, 2 Aug 2023 00:01:16 +0800
From: Baoquan He <bhe@...hat.com>
To: Lorenzo Stoakes <lstoakes@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Uladzislau Rezki <urezki@...il.com>,
linux-fsdevel@...r.kernel.org, Jiri Olsa <olsajiri@...il.com>,
Will Deacon <will@...nel.org>, Mike Galbraith <efault@....de>,
Mark Rutland <mark.rutland@....com>,
wangkefeng.wang@...wei.com, catalin.marinas@....com,
ardb@...nel.org, David Hildenbrand <david@...hat.com>,
Linux regression tracking <regressions@...mhuis.info>,
regressions@...ts.linux.dev, Matthew Wilcox <willy@...radead.org>,
Liu Shixin <liushixin2@...wei.com>,
Jens Axboe <axboe@...nel.dk>,
Alexander Viro <viro@...iv.linux.org.uk>,
stable@...r.kernel.org
Subject: Re: [PATCH] fs/proc/kcore: reinstate bounce buffer for KCORE_TEXT
regions
On 08/01/23 at 11:57pm, Baoquan He wrote:
> On 07/31/23 at 10:50pm, Lorenzo Stoakes wrote:
> > Some architectures do not populate the entire range categorised by
> > KCORE_TEXT, so we must ensure that the kernel address we read from is
> > valid.
> >
> > Unfortunately there is no solution currently available to do so with a
> > purely iterator solution so reinstate the bounce buffer in this instance so
> > we can use copy_from_kernel_nofault() in order to avoid page faults when
> > regions are unmapped.
> >
> > This change partly reverts commit 2e1c0170771e ("fs/proc/kcore: avoid
> > bounce buffer for ktext data"), reinstating the bounce buffer, but adapts
> > the code to continue to use an iterator.
> >
> > Fixes: 2e1c0170771e ("fs/proc/kcore: avoid bounce buffer for ktext data")
> > Reported-by: Jiri Olsa <olsajiri@...il.com>
> > Closes: https://lore.kernel.org/all/ZHc2fm+9daF6cgCE@krava
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> > ---
> > fs/proc/kcore.c | 26 +++++++++++++++++++++++++-
> > 1 file changed, 25 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> > index 9cb32e1a78a0..3bc689038232 100644
> > --- a/fs/proc/kcore.c
> > +++ b/fs/proc/kcore.c
> > @@ -309,6 +309,8 @@ static void append_kcore_note(char *notes, size_t *i, const char *name,
> >
> > static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
> > {
> > + struct file *file = iocb->ki_filp;
> > + char *buf = file->private_data;
> > loff_t *fpos = &iocb->ki_pos;
> > size_t phdrs_offset, notes_offset, data_offset;
> > size_t page_offline_frozen = 1;
> > @@ -554,11 +556,22 @@ static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
> > fallthrough;
> > case KCORE_VMEMMAP:
> > case KCORE_TEXT:
> > + /*
> > + * Sadly we must use a bounce buffer here to be able to
> > + * make use of copy_from_kernel_nofault(), as these
> > + * memory regions might not always be mapped on all
> > + * architectures.
> > + */
> > + if (copy_from_kernel_nofault(buf, (void *)start, tsz)) {
> > + if (iov_iter_zero(tsz, iter) != tsz) {
> > + ret = -EFAULT;
> > + goto out;
> > + }
> > /*
> > * We use _copy_to_iter() to bypass usermode hardening
> > * which would otherwise prevent this operation.
> > */
> > - if (_copy_to_iter((char *)start, tsz, iter) != tsz) {
> > + } else if (_copy_to_iter(buf, tsz, iter) != tsz) {
> > ret = -EFAULT;
> > goto out;
> > }
> > @@ -595,6 +608,10 @@ static int open_kcore(struct inode *inode, struct file *filp)
> > if (ret)
> > return ret;
> >
> > + filp->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > + if (!filp->private_data)
> > + return -ENOMEM;
> > +
> > if (kcore_need_update)
> > kcore_update_ram();
> > if (i_size_read(inode) != proc_root_kcore->size) {
> > @@ -605,9 +622,16 @@ static int open_kcore(struct inode *inode, struct file *filp)
> > return 0;
> > }
> >
> > +static int release_kcore(struct inode *inode, struct file *file)
> > +{
> > + kfree(file->private_data);
> > + return 0;
> > +}
> > +
> > static const struct proc_ops kcore_proc_ops = {
> > .proc_read_iter = read_kcore_iter,
> > .proc_open = open_kcore,
> > + .proc_release = release_kcore,
> > .proc_lseek = default_llseek,
> > };
>
> On 6.5-rc4, the failures can be reproduced stably on a arm64 machine.
> With patch applied, both makedumpfile and objdump test cases passed.
>
> And the code change looks good to me, thanks.
>
> Tested-by: Baoquan He <bhe@...hat.com>
> Reviewed-by: Baoquan He <bhe@...hat.com>
>
>
> ===============================================
> [root@ ~]# makedumpfile --mem-usage /proc/kcore
> The kernel version is not supported.
> The makedumpfile operation may be incomplete.
>
> TYPE PAGES EXCLUDABLE DESCRIPTION
> ----------------------------------------------------------------------
> ZERO 76234 yes Pages filled with zero
> NON_PRI_CACHE 147613 yes Cache pages without private flag
> PRI_CACHE 3847 yes Cache pages with private flag
> USER 15276 yes User process pages
> FREE 15809884 yes Free pages
> KERN_DATA 459950 no Dumpable kernel data
>
> page size: 4096
> Total pages on system: 16512804
> Total size on system: 67636445184 Byte
>
> [root@ ~]# objdump -d --start-address=0x^C
> [root@ ~]# cat /proc/kallsyms | grep ksys_read
> ffffab3be77229d8 T ksys_readahead
> ffffab3be782a700 T ksys_read
> [root@ ~]# objdump -d --start-address=0xffffab3be782a700 --stop-address=0xffffab3be782a710 /proc/kcore
>
> /proc/kcore: file format elf64-littleaarch64
>
>
> Disassembly of section load1:
>
> ffffab3be782a700 <load1+0x41a700>:
> ffffab3be782a700: aa1e03e9 mov x9, x30
> ffffab3be782a704: d503201f nop
> ffffab3be782a708: d503233f paciasp
> ffffab3be782a70c: a9bc7bfd stp x29, x30, [sp, #-64]!
> objdump: error: /proc/kcore(load2) is too large (0x7bff70000000 bytes)
> objdump: Reading section load2 failed because: memory exhausted
By the way, I can still see the objdump error saying kcore is too large
as above, at the same time there's console printing as below. Haven't
checked it's objdump's issue or kernel's.
[ 6631.575800] __vm_enough_memory: pid: 5321, comm: objdump, not enough memory for the allocation
[ 6631.584469] __vm_enough_memory: pid: 5321, comm: objdump, not enough memory for the allocation
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