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linux-user: Handle short reads in mmap_h_gt_g

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In particular, if an image has a large bss, we can hit
EOF before reading all host_len bytes of the mapping.

Create a helper, mmap_pread to handle the job for both
the larger block in mmap_h_gt_g itself, as well as the
smaller block in mmap_frag.

Cc: qemu-stable@nongnu.org
Fixes: eb5027ac61 ("linux-user: Split out mmap_h_gt_g")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2504
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240820050848.165253-2-richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
This commit is contained in:
Richard Henderson 2024-08-16 07:13:31 +10:00
parent 9eb5bfbe33
commit a4ad4a9d98
1 changed files with 38 additions and 6 deletions
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42
linux-user/mmap.c
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@ -283,6 +283,40 @@ static int do_munmap(void *addr, size_t len)
return munmap(addr, len);
}
/*
* Perform a pread on behalf of target_mmap. We can reach EOF, we can be
* interrupted by signals, and in general there's no good error return path.
* If @zero, zero the rest of the block at EOF.
* Return true on success.
*/
static bool mmap_pread(int fd, void *p, size_t len, off_t offset, bool zero)
{
while (1) {
ssize_t r = pread(fd, p, len, offset);
if (likely(r == len)) {
/* Complete */
return true;
}
if (r == 0) {
/* EOF */
if (zero) {
memset(p, 0, len);
}
return true;
}
if (r > 0) {
/* Short read */
p += r;
len -= r;
offset += r;
} else if (errno != EINTR) {
/* Error */
return false;
}
}
}
/*
* Map an incomplete host page.
*
@ -357,11 +391,10 @@ static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
/* Read or zero the new guest pages. */
if (flags & MAP_ANONYMOUS) {
memset(g2h_untagged(start), 0, last - start + 1);
} else {
if (pread(fd, g2h_untagged(start), last - start + 1, offset) == -1) {
} else if (!mmap_pread(fd, g2h_untagged(start), last - start + 1,
offset, true)) {
return false;
}
}
/* Put final protection */
if (host_prot_new != host_prot_old) {
@ -853,8 +886,7 @@ static abi_long mmap_h_gt_g(abi_ulong start, abi_ulong len,
}
if (misaligned_offset) {
/* TODO: The read could be short. */
if (pread(fd, p, host_len, offset + real_start - start) != host_len) {
if (!mmap_pread(fd, p, host_len, offset + real_start - start, false)) {
do_munmap(p, host_len);
return -1;
}