From cb48d5d1592e63ebd0d4a3e300ef98e38e6306d7 Mon Sep 17 00:00:00 2001 From: Richard Henderson 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 Signed-off-by: Richard Purdie --- 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