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From cb48d5d1592e63ebd0d4a3e300ef98e38e6306d7 Mon Sep 17 00:00:00 2001
From: Richard Henderson <richard.henderson@linaro.org>
Date: Wed, 28 Feb 2024 10:25:17 -1000
Subject: [PATCH 4/5] linux-user: Rewrite target_shmat
Handle combined host and guest alignment requirements.
Handle host and guest page size differences.
Handle SHM_EXEC.
Upstream-Status: Submitted [https://www.mail-archive.com/qemu-devel@nongnu.org/msg1026793.html]
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/115
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
---
linux-user/mmap.c | 166 +++++++++++++++++++++++++++++++++++++---------
1 file changed, 133 insertions(+), 33 deletions(-)
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 18fb3aaf7..6a2f649bb 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -1062,69 +1062,161 @@ static inline abi_ulong target_shmlba(CPUArchState *cpu_env)
}
#endif
+#if defined(__arm__) || defined(__mips__) || defined(__sparc__)
+#define HOST_FORCE_SHMLBA 1
+#else
+#define HOST_FORCE_SHMLBA 0
+#endif
+
abi_ulong target_shmat(CPUArchState *cpu_env, int shmid,
abi_ulong shmaddr, int shmflg)
{
CPUState *cpu = env_cpu(cpu_env);
- abi_ulong raddr;
struct shmid_ds shm_info;
int ret;
- abi_ulong shmlba;
+ int h_pagesize;
+ int t_shmlba, h_shmlba, m_shmlba;
+ size_t t_len, h_len, m_len;
/* shmat pointers are always untagged */
- /* find out the length of the shared memory segment */
+ /*
+ * Because we can't use host shmat() unless the address is sufficiently
+ * aligned for the host, we'll need to check both.
+ * TODO: Could be fixed with softmmu.
+ */
+ t_shmlba = target_shmlba(cpu_env);
+ h_pagesize = qemu_real_host_page_size();
+ h_shmlba = (HOST_FORCE_SHMLBA ? SHMLBA : h_pagesize);
+ m_shmlba = MAX(t_shmlba, h_shmlba);
+
+ if (shmaddr) {
+ if (shmaddr & (m_shmlba - 1)) {
+ if (shmflg & SHM_RND) {
+ /*
+ * The guest is allowing the kernel to round the address.
+ * Assume that the guest is ok with us rounding to the
+ * host required alignment too. Anyway if we don't, we'll
+ * get an error from the kernel.
+ */
+ shmaddr &= ~(m_shmlba - 1);
+ if (shmaddr == 0 && (shmflg & SHM_REMAP)) {
+ return -TARGET_EINVAL;
+ }
+ } else {
+ int require = TARGET_PAGE_SIZE;
+#ifdef TARGET_FORCE_SHMLBA
+ require = t_shmlba;
+#endif
+ /*
+ * Include host required alignment, as otherwise we cannot
+ * use host shmat at all.
+ */
+ require = MAX(require, h_shmlba);
+ if (shmaddr & (require - 1)) {
+ return -TARGET_EINVAL;
+ }
+ }
+ }
+ } else {
+ if (shmflg & SHM_REMAP) {
+ return -TARGET_EINVAL;
+ }
+ }
+ /* All rounding now manually concluded. */
+ shmflg &= ~SHM_RND;
+
+ /* Find out the length of the shared memory segment. */
ret = get_errno(shmctl(shmid, IPC_STAT, &shm_info));
if (is_error(ret)) {
/* can't get length, bail out */
return ret;
}
+ t_len = TARGET_PAGE_ALIGN(shm_info.shm_segsz);
+ h_len = ROUND_UP(shm_info.shm_segsz, h_pagesize);
+ m_len = MAX(t_len, h_len);
- shmlba = target_shmlba(cpu_env);
-
- if (shmaddr & (shmlba - 1)) {
- if (shmflg & SHM_RND) {
- shmaddr &= ~(shmlba - 1);
- } else {
- return -TARGET_EINVAL;
- }
- }
- if (!guest_range_valid_untagged(shmaddr, shm_info.shm_segsz)) {
+ if (!guest_range_valid_untagged(shmaddr, m_len)) {
return -TARGET_EINVAL;
}
WITH_MMAP_LOCK_GUARD() {
- void *host_raddr;
+ bool mapped = false;
+ void *want, *test;
abi_ulong last;
- if (shmaddr) {
- host_raddr = shmat(shmid, (void *)g2h_untagged(shmaddr), shmflg);
+ if (!shmaddr) {
+ shmaddr = mmap_find_vma(0, m_len, m_shmlba);
+ if (shmaddr == -1) {
+ return -TARGET_ENOMEM;
+ }
+ mapped = !reserved_va;
+ } else if (shmflg & SHM_REMAP) {
+ /*
+ * If host page size > target page size, the host shmat may map
+ * more memory than the guest expects. Reject a mapping that
+ * would replace memory in the unexpected gap.
+ * TODO: Could be fixed with softmmu.
+ */
+ if (t_len < h_len &&
+ !page_check_range_empty(shmaddr + t_len,
+ shmaddr + h_len - 1)) {
+ return -TARGET_EINVAL;
+ }
} else {
- abi_ulong mmap_start;
+ if (!page_check_range_empty(shmaddr, shmaddr + m_len - 1)) {
+ return -TARGET_EINVAL;
+ }
+ }
- /* In order to use the host shmat, we need to honor host SHMLBA. */
- mmap_start = mmap_find_vma(0, shm_info.shm_segsz,
- MAX(SHMLBA, shmlba));
+ /* All placement is now complete. */
+ want = (void *)g2h_untagged(shmaddr);
- if (mmap_start == -1) {
- return -TARGET_ENOMEM;
+ /*
+ * Map anonymous pages across the entire range, then remap with
+ * the shared memory. This is required for a number of corner
+ * cases for which host and guest page sizes differ.
+ */
+ if (h_len != t_len) {
+ int mmap_p = PROT_READ | (shmflg & SHM_RDONLY ? 0 : PROT_WRITE);
+ int mmap_f = MAP_PRIVATE | MAP_ANONYMOUS
+ | (reserved_va || (shmflg & SHM_REMAP)
+ ? MAP_FIXED : MAP_FIXED_NOREPLACE);
+
+ test = mmap(want, m_len, mmap_p, mmap_f, -1, 0);
+ if (unlikely(test != want)) {
+ /* shmat returns EINVAL not EEXIST like mmap. */
+ ret = (test == MAP_FAILED && errno != EEXIST
+ ? get_errno(-1) : -TARGET_EINVAL);
+ if (mapped) {
+ do_munmap(want, m_len);
+ }
+ return ret;
}
- host_raddr = shmat(shmid, g2h_untagged(mmap_start),
- shmflg | SHM_REMAP);
+ mapped = true;
}
- if (host_raddr == (void *)-1) {
- return get_errno(-1);
+ if (reserved_va || mapped) {
+ shmflg |= SHM_REMAP;
+ }
+ test = shmat(shmid, want, shmflg);
+ if (test == MAP_FAILED) {
+ ret = get_errno(-1);
+ if (mapped) {
+ do_munmap(want, m_len);
+ }
+ return ret;
}
- raddr = h2g(host_raddr);
- last = raddr + shm_info.shm_segsz - 1;
+ assert(test == want);
- page_set_flags(raddr, last,
+ last = shmaddr + m_len - 1;
+ page_set_flags(shmaddr, last,
PAGE_VALID | PAGE_RESET | PAGE_READ |
- (shmflg & SHM_RDONLY ? 0 : PAGE_WRITE));
+ (shmflg & SHM_RDONLY ? 0 : PAGE_WRITE) |
+ (shmflg & SHM_EXEC ? PAGE_EXEC : 0));
- shm_region_rm_complete(raddr, last);
- shm_region_add(raddr, last);
+ shm_region_rm_complete(shmaddr, last);
+ shm_region_add(shmaddr, last);
}
/*
@@ -1138,7 +1230,15 @@ abi_ulong target_shmat(CPUArchState *cpu_env, int shmid,
tb_flush(cpu);
}
- return raddr;
+ if (qemu_loglevel_mask(CPU_LOG_PAGE)) {
+ FILE *f = qemu_log_trylock();
+ if (f) {
+ fprintf(f, "page layout changed following shmat\n");
+ page_dump(f);
+ qemu_log_unlock(f);
+ }
+ }
+ return shmaddr;
}
abi_long target_shmdt(abi_ulong shmaddr)
--
2.34.1
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