Hi Philippe,
On Thu, Nov 11, 2021 at 03:55:48PM +0100, Philippe Mathieu-Daudé wrote:
> Hi Jamie,
>
> On 11/11/21 15:11, Jamie Iles wrote:
> > On Linux, read() will only ever read a maximum of 0x7ffff000 bytes
> > regardless of what is asked. If the file is larger than 0x7ffff000
> > bytes the read will need to be broken up into multiple chunks.
> >
> > Cc: Luc Michel <lmic...@kalray.eu>
> > Signed-off-by: Jamie Iles <ja...@nuviainc.com>
> > ---
> > hw/core/loader.c | 40 ++++++++++++++++++++++++++++++++++------
> > 1 file changed, 34 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/core/loader.c b/hw/core/loader.c
> > index 348bbf535bd9..16ca9b99cf0f 100644
> > --- a/hw/core/loader.c
> > +++ b/hw/core/loader.c
> > @@ -80,6 +80,34 @@ int64_t get_image_size(const char *filename)
> > return size;
> > }
> >
> > +static ssize_t read_large(int fd, void *dst, size_t len)
> > +{
> > + /*
> > + * man 2 read says:
> > + *
> > + * On Linux, read() (and similar system calls) will transfer at most
> > + * 0x7ffff000 (2,147,479,552) bytes, returning the number of bytes
>
> Could you mention MAX_RW_COUNT from linux/fs.h?
>
> > + * actually transferred. (This is true on both 32-bit and 64-bit
> > + * systems.)
>
> Maybe "This is true for both ILP32 and LP64 data models used by Linux"?
> (because that would not be the case for the ILP64 model).
>
> Otherwise s/systems/Linux variants/?
>
> > + *
> > + * So read in chunks no larger than 0x7ffff000 bytes.
> > + */
> > + size_t max_chunk_size = 0x7ffff000;
>
> We can declare it static const.
Ack, can fix all of those up.
> > + size_t offset = 0;
> > +
> > + while (offset < len) {
> > + size_t chunk_len = MIN(max_chunk_size, len - offset);
> > + ssize_t br = read(fd, dst + offset, chunk_len);
> > +
> > + if (br < 0) {
> > + return br;
> > + }
> > + offset += br;
> > + }
> > +
> > + return (ssize_t)len;
> > +}
>
> I see other read()/pread() calls:
>
> hw/9pfs/9p-local.c:472: tsize = read(fd, (void *)buf, bufsz);
> hw/vfio/common.c:269: if (pread(vbasedev->fd, &buf, size,
> region->fd_offset + addr) != size) {
> ...
>
> Maybe the read_large() belongs to "sysemu/os-xxx.h"?
I think util/osdep.c would be a good fit for this. To make sure we're
on the same page though are you proposing converting all pread/read
calls to a qemu variant or auditing for ones that could potentially take
a larger size?
Thanks,
Jamie
