[PATCH v3] fs: semihosting: Fixup smh_flen and smh_read against overflow
Sean Anderson
sean.anderson at seco.com
Fri Oct 10 23:05:43 CEST 2025
On 10/10/25 16:55, Sean Anderson wrote:
> On 10/10/25 16:31, Tom Rini wrote:
>> On Fri, Oct 03, 2025 at 10:03:57AM +0100, Andrew Goodbody wrote:
>>
>>> The sys calls SYS_FLEN and SYS_READ were being used in a way that did
>>> not allow for file sizes > 2^31. Fixing this required changing the
>>> signatures of the functions smh_flen and smh_read to allow file
>>> sizes up to 2^32 - 2 and also being able to return errors that could be
>>> tested for.
>>>
>>> This issue was found by Smatch.
>
> IMO this makes the API more awkward for no benefit, as no one actually
> needs to read 2-4 GiB files (but no larger) with this interface. Aside
> from this being unimaginably slow on real hardware and inferior to
> virtio on emulated hardware, there are still other problems. Like, how
> are you even going to address the RAM on a 32-bit system? U-Boot
> (AFAIK) only does a linear mapping and most highmem systems will not
> even have more than 1-2 GiB of memory without mapping over devices.
>
> I think a much cleaner solution is to just limit lengths to 2 GiB where
> appropriate.
>
>>> Signed-off-by: Andrew Goodbody <andrew.goodbody at linaro.org>
>>> ---
>>> Changes in v3:
>>> - V2 missed fixing up one use of smh_flen, fix it
>>> - Link to v2: https://cas5-0-urlprotect.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2flore.kernel.org%2fr%2f20251002%2dfs%5fsemihosting%2dv2%2d1%2dc1783e4188d8%40linaro.org&umid=65083f76-83f6-4254-a979-8e43c1e3a788&rct=1760129739&auth=d807158c60b7d2502abde8a2fc01f40662980862-31b6b7517dcc163c67b790b33a34a4f0a3f321b7
>>>
>>> Changes in v2:
>>> - Fixup smh_flen and smh_read to allow for > 2^31 byte files
>>> - Link to v1: https://cas5-0-urlprotect.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2flore.kernel.org%2fr%2f20251002%2dfs%5fsemihosting%2dv1%2d1%2d1124e6becc51%40linaro.org&umid=65083f76-83f6-4254-a979-8e43c1e3a788&rct=1760129739&auth=d807158c60b7d2502abde8a2fc01f40662980862-38e52356997cde7f2ae1d272bd8f35d6bface016
>>> ---
>>> common/spl/spl_semihosting.c | 13 +++++++------
>>> drivers/serial/serial_semihosting.c | 6 ++++--
>>> fs/semihostingfs.c | 23 +++++++++++++----------
>>> include/semihosting.h | 13 +++++++------
>>> lib/semihosting.c | 25 +++++++++++++++++++------
>>> 5 files changed, 50 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/common/spl/spl_semihosting.c b/common/spl/spl_semihosting.c
>>> index f36863fe48d25859ee9af67a67140893b6e9e262..fb578a274d0d937b2ed5bd13e505bcefd4491799 100644
>>> --- a/common/spl/spl_semihosting.c
>>> +++ b/common/spl/spl_semihosting.c
>>> @@ -13,13 +13,14 @@ static ulong smh_fit_read(struct spl_load_info *load, ulong file_offset,
>>> ulong size, void *buf)
>>> {
>>> long fd = *(long *)load->priv;
>>> - ulong ret;
>>> + long ret;
>>> + size_t bytes_read;
>>>
>>> if (smh_seek(fd, file_offset))
>>> return 0;
>>>
>>> - ret = smh_read(fd, buf, size);
>>> - return ret < 0 ? 0 : ret;
>>> + ret = smh_read(fd, buf, size, &bytes_read);
>>> + return ret < 0 ? 0 : bytes_read;
>>> }
>>>
>>> static int spl_smh_load_image(struct spl_image_info *spl_image,
>>> @@ -27,7 +28,8 @@ static int spl_smh_load_image(struct spl_image_info *spl_image,
>>> {
>>> const char *filename = CONFIG_SPL_FS_LOAD_PAYLOAD_NAME;
>>> int ret;
>>> - long fd, len;
>>> + long fd;
>>> + size_t len;
>>> struct spl_load_info load;
>>>
>>> fd = smh_open(filename, MODE_READ | MODE_BINARY);
>>> @@ -36,12 +38,11 @@ static int spl_smh_load_image(struct spl_image_info *spl_image,
>>> return fd;
>>> }
>>>
>>> - ret = smh_flen(fd);
>>> + ret = smh_flen(fd, &len);
>>> if (ret < 0) {
>>> log_debug("could not get length of image: %d\n", ret);
>>> goto out;
>>> }
>>> - len = ret;
>>>
>>> spl_load_init(&load, smh_fit_read, &fd, 1);
>>> ret = spl_load(spl_image, bootdev, &load, len, 0);
>>> diff --git a/drivers/serial/serial_semihosting.c b/drivers/serial/serial_semihosting.c
>>> index 56a5ec72428afdd97eccad739a46189380ba3e76..017b1f8eda84f5c25e09be7e970d0ebfdbf2ace0 100644
>>> --- a/drivers/serial/serial_semihosting.c
>>> +++ b/drivers/serial/serial_semihosting.c
>>> @@ -25,11 +25,12 @@ static int smh_serial_getc(struct udevice *dev)
>>> {
>>> char ch = 0;
>>> struct smh_serial_priv *priv = dev_get_priv(dev);
>>> + size_t bytes_read;
>>>
>>> if (priv->infd < 0)
>>> return smh_getc();
>>>
>>> - smh_read(priv->infd, &ch, sizeof(ch));
>>> + smh_read(priv->infd, &ch, sizeof(ch), &bytes_read);
>>> return ch;
>>> }
>>>
>>> @@ -140,11 +141,12 @@ static void smh_serial_setbrg(void)
>>> static int smh_serial_getc(void)
>>> {
>>> char ch = 0;
>>> + size_t bytes_read;
>>>
>>> if (infd < 0)
>>> return smh_getc();
>>>
>>> - smh_read(infd, &ch, sizeof(ch));
>>> + smh_read(infd, &ch, sizeof(ch), &bytes_read);
>>> return ch;
>>> }
>>>
>>> diff --git a/fs/semihostingfs.c b/fs/semihostingfs.c
>>> index 77e39ca407e4d240a1fd573497c5b6b908816454..6a4d0aaaf2fdaf8da154e59677839a5c7a4889e9 100644
>>> --- a/fs/semihostingfs.c
>>> +++ b/fs/semihostingfs.c
>>> @@ -23,7 +23,8 @@ int smh_fs_set_blk_dev(struct blk_desc *rbdd, struct disk_partition *info)
>>> static int smh_fs_read_at(const char *filename, loff_t pos, void *buffer,
>>> loff_t maxsize, loff_t *actread)
>>> {
>>> - long fd, size, ret;
>>> + long fd, ret;
>>> + size_t size;
>>>
>>> fd = smh_open(filename, MODE_READ | MODE_BINARY);
>>> if (fd < 0)
>>> @@ -34,19 +35,19 @@ static int smh_fs_read_at(const char *filename, loff_t pos, void *buffer,
>>> return ret;
>>> }
>>> if (!maxsize) {
>>> - size = smh_flen(fd);
>>> + ret = smh_flen(fd, &size);
>>> if (ret < 0) {
>>> smh_close(fd);
>>> - return size;
>>> + return ret;
>>> }
>>>
>>> maxsize = size;
>>> }
>>>
>>> - size = smh_read(fd, buffer, maxsize);
>>> + ret = smh_read(fd, buffer, maxsize, &size);
>>> smh_close(fd);
>>> - if (size < 0)
>>> - return size;
>>> + if (ret < 0)
>>> + return ret;
>>>
>>> *actread = size;
>>> return 0;
>>> @@ -78,17 +79,19 @@ static int smh_fs_write_at(const char *filename, loff_t pos, void *buffer,
>>>
>>> int smh_fs_size(const char *filename, loff_t *result)
>>> {
>>> - long fd, size;
>>> + long fd;
>>> + size_t size;
>>> + int ret;
>>>
>>> fd = smh_open(filename, MODE_READ | MODE_BINARY);
>>> if (fd < 0)
>>> return fd;
>>>
>>> - size = smh_flen(fd);
>>> + ret = smh_flen(fd, &size);
>>> smh_close(fd);
>>>
>>> - if (size < 0)
>>> - return size;
>>> + if (ret < 0)
>>> + return ret;
>>>
>>> *result = size;
>>> return 0;
>>> diff --git a/include/semihosting.h b/include/semihosting.h
>>> index 4e844cbad87bb1ae6bb365f87f3e7a8aeea445f4..60535199b9532ce16620aea3ca1ea741c5b73766 100644
>>> --- a/include/semihosting.h
>>> +++ b/include/semihosting.h
>>> @@ -95,12 +95,12 @@ long smh_open(const char *fname, enum smh_open_mode mode);
>>> * @fd: A file descriptor returned from smh_open()
>>> * @memp: Pointer to a buffer of memory of at least @len bytes
>>> * @len: The number of bytes to read
>>> + * @read_len: Pointer which will be updated with actual bytes read on success,
>>> + * with 0 indicating %EOF
>>> *
>>> - * Return:
>>> - * * The number of bytes read on success, with 0 indicating %EOF
>>> - * * A negative error on failure
>>> + * Return: 0 on success or negative error on failure
>>> */
>>> -long smh_read(long fd, void *memp, size_t len);
>>> +long smh_read(long fd, void *memp, size_t len, size_t *read_len);
>>>
>>> /**
>>> * smh_write() - Write data to a file
>>> @@ -124,10 +124,11 @@ long smh_close(long fd);
>>> /**
>>> * smh_flen() - Get the length of a file
>>> * @fd: A file descriptor returned from smh_open()
>>> + * @size: Pointer which will be updated with length of file on success
>>> *
>>> - * Return: The length of the file, in bytes, or a negative error on failure
>>> + * Return: 0 on success or negative error on failure
>>> */
>>> -long smh_flen(long fd);
>>> +int smh_flen(long fd, size_t *size);
>>>
>>> /**
>>> * smh_seek() - Seek to a position in a file
>>> diff --git a/lib/semihosting.c b/lib/semihosting.c
>>> index 9be5bffd30124777c4f8110065e6cca5640312ac..a0f42d41e4a7ad95023c684f6824bfc677ad25cd 100644
>>> --- a/lib/semihosting.c
>>> +++ b/lib/semihosting.c
>>> @@ -93,9 +93,9 @@ struct smh_rdwr_s {
>>> size_t len;
>>> };
>>>
>>> -long smh_read(long fd, void *memp, size_t len)
>>> +long smh_read(long fd, void *memp, size_t len, size_t *read_len)
>
> But really we just need to make this return size_t.
>
>>> {
>>> - long ret;
>>> + size_t ret;
>>> struct smh_rdwr_s read;
>>>
>>> debug("%s: fd %ld, memp %p, len %zu\n", __func__, fd, memp, len);
>>> @@ -105,9 +105,20 @@ long smh_read(long fd, void *memp, size_t len)
>>> read.len = len;
>>>
>>> ret = smh_trap(SYSREAD, &read);
>
> This is a separate fix. Please break it out into another patch.
And actually, this is wrong since QEMU and OpenOCD both return -1 on error
and set errno. So you need a fourth branch when ret == -1. So maybe we
should just check for len > LONG_MAX on function entry and return
-EOVERFLOW right away.
>>> - if (ret < 0)
>>> + if (!ret) {
>>> + /* Success */
>>> + *read_len = len;
>>> + return 0;
>>> + } else if (ret == len) {
>>> + /* EOF */
>>> + *read_len = 0;
>>> + return 0;
>>> + } else {
>>> + /* Partial success */
>>> + *read_len = len - ret;
>>> return smh_errno();
smh_errno() tends to only be set on failure. So if you call it on
a short read you may get a spurious error.
>>> - return len - ret;
>>> + }
>>> +
>>> }
>>>
>>> long smh_write(long fd, const void *memp, size_t len, ulong *written)
>>> @@ -140,7 +151,7 @@ long smh_close(long fd)
>>> return 0;
>>> }
>>>
>>> -long smh_flen(long fd)
>>> +int smh_flen(long fd, size_t *size)
>>> {
>>> long ret;
>>>
>>> @@ -149,7 +160,9 @@ long smh_flen(long fd)
>>> ret = smh_trap(SYSFLEN, &fd);
>>> if (ret == -1)
>
> Just change this to
>
> if (ret < 0)
> return ret == -1 ? smh_errno() : -EOVERFLOW;
>
> And now all the existing code works.
>
>>> return smh_errno();
>>> - return ret;
>>> +
>>> + *size = (size_t)ret;
>>> + return 0;
>
>>> }
>>>
>>> long smh_seek(long fd, long pos)
>>>
>>
>> There was (as good thing!) much review and feedback on v1 and v2. Is
>> everyone happy now with v3? Thanks!
>>
>
> Sorry for the delay, I'm not working on U-Boot at $WORK at all right now
> so I don't have much time for review.
>
> --Sean
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