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qemu/linux-user/mmap.c
Richard Henderson 26bab757d4 linux-user: Introduce PAGE_ANON 
Record whether the backing page is anonymous, or if it has file
backing.  This will allow us to get close to the Linux AArch64
ABI for MTE, which allows tag memory only on ram-backed VMAs.

The real ABI allows tag memory on files, when those files are
on ram-backed filesystems, such as tmpfs.  We will not be able
to implement that in QEMU linux-user.

Thankfully, anonymous memory for malloc arenas is the primary
consumer of this feature, so this restricted version should
still be of use.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210212184902.1251044-3-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2021-02-16 11:04:53 +00:00

808 lines
25 KiB
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/*
* mmap support for qemu
*
* Copyright (c) 2003 Fabrice Bellard
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "exec/log.h"
#include "qemu.h"
static pthread_mutex_t mmap_mutex = PTHREAD_MUTEX_INITIALIZER;
static __thread int mmap_lock_count;
void mmap_lock(void)
{
if (mmap_lock_count++ == 0) {
pthread_mutex_lock(&mmap_mutex);
}
}
void mmap_unlock(void)
{
if (--mmap_lock_count == 0) {
pthread_mutex_unlock(&mmap_mutex);
}
}
bool have_mmap_lock(void)
{
return mmap_lock_count > 0 ? true : false;
}
/* Grab lock to make sure things are in a consistent state after fork(). */
void mmap_fork_start(void)
{
if (mmap_lock_count)
abort();
pthread_mutex_lock(&mmap_mutex);
}
void mmap_fork_end(int child)
{
if (child)
pthread_mutex_init(&mmap_mutex, NULL);
else
pthread_mutex_unlock(&mmap_mutex);
}
/*
* Validate target prot bitmask.
* Return the prot bitmask for the host in *HOST_PROT.
* Return 0 if the target prot bitmask is invalid, otherwise
* the internal qemu page_flags (which will include PAGE_VALID).
*/
static int validate_prot_to_pageflags(int *host_prot, int prot)
{
int valid = PROT_READ | PROT_WRITE | PROT_EXEC | TARGET_PROT_SEM;
int page_flags = (prot & PAGE_BITS) | PAGE_VALID;
/*
* For the host, we need not pass anything except read/write/exec.
* While PROT_SEM is allowed by all hosts, it is also ignored, so
* don't bother transforming guest bit to host bit. Any other
* target-specific prot bits will not be understood by the host
* and will need to be encoded into page_flags for qemu emulation.
*
* Pages that are executable by the guest will never be executed
* by the host, but the host will need to be able to read them.
*/
*host_prot = (prot & (PROT_READ | PROT_WRITE))
| (prot & PROT_EXEC ? PROT_READ : 0);
#ifdef TARGET_AARCH64
/*
* The PROT_BTI bit is only accepted if the cpu supports the feature.
* Since this is the unusual case, don't bother checking unless
* the bit has been requested. If set and valid, record the bit
* within QEMU's page_flags.
*/
if (prot & TARGET_PROT_BTI) {
ARMCPU *cpu = ARM_CPU(thread_cpu);
if (cpu_isar_feature(aa64_bti, cpu)) {
valid |= TARGET_PROT_BTI;
page_flags |= PAGE_BTI;
}
}
#endif
return prot & ~valid ? 0 : page_flags;
}
/* NOTE: all the constants are the HOST ones, but addresses are target. */
int target_mprotect(abi_ulong start, abi_ulong len, int target_prot)
{
abi_ulong end, host_start, host_end, addr;
int prot1, ret, page_flags, host_prot;
trace_target_mprotect(start, len, target_prot);
if ((start & ~TARGET_PAGE_MASK) != 0) {
return -TARGET_EINVAL;
}
page_flags = validate_prot_to_pageflags(&host_prot, target_prot);
if (!page_flags) {
return -TARGET_EINVAL;
}
len = TARGET_PAGE_ALIGN(len);
end = start + len;
if (!guest_range_valid(start, len)) {
return -TARGET_ENOMEM;
}
if (len == 0) {
return 0;
}
mmap_lock();
host_start = start & qemu_host_page_mask;
host_end = HOST_PAGE_ALIGN(end);
if (start > host_start) {
/* handle host page containing start */
prot1 = host_prot;
for (addr = host_start; addr < start; addr += TARGET_PAGE_SIZE) {
prot1 |= page_get_flags(addr);
}
if (host_end == host_start + qemu_host_page_size) {
for (addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
prot1 |= page_get_flags(addr);
}
end = host_end;
}
ret = mprotect(g2h(host_start), qemu_host_page_size,
prot1 & PAGE_BITS);
if (ret != 0) {
goto error;
}
host_start += qemu_host_page_size;
}
if (end < host_end) {
prot1 = host_prot;
for (addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
prot1 |= page_get_flags(addr);
}
ret = mprotect(g2h(host_end - qemu_host_page_size),
qemu_host_page_size, prot1 & PAGE_BITS);
if (ret != 0) {
goto error;
}
host_end -= qemu_host_page_size;
}
/* handle the pages in the middle */
if (host_start < host_end) {
ret = mprotect(g2h(host_start), host_end - host_start, host_prot);
if (ret != 0) {
goto error;
}
}
page_set_flags(start, start + len, page_flags);
mmap_unlock();
return 0;
error:
mmap_unlock();
return ret;
}
/* map an incomplete host page */
static int mmap_frag(abi_ulong real_start,
abi_ulong start, abi_ulong end,
int prot, int flags, int fd, abi_ulong offset)
{
abi_ulong real_end, addr;
void *host_start;
int prot1, prot_new;
real_end = real_start + qemu_host_page_size;
host_start = g2h(real_start);
/* get the protection of the target pages outside the mapping */
prot1 = 0;
for(addr = real_start; addr < real_end; addr++) {
if (addr < start || addr >= end)
prot1 |= page_get_flags(addr);
}
if (prot1 == 0) {
/* no page was there, so we allocate one */
void *p = mmap(host_start, qemu_host_page_size, prot,
flags | MAP_ANONYMOUS, -1, 0);
if (p == MAP_FAILED)
return -1;
prot1 = prot;
}
prot1 &= PAGE_BITS;
prot_new = prot | prot1;
if (!(flags & MAP_ANONYMOUS)) {
/* msync() won't work here, so we return an error if write is
possible while it is a shared mapping */
if ((flags & MAP_TYPE) == MAP_SHARED &&
(prot & PROT_WRITE))
return -1;
/* adjust protection to be able to read */
if (!(prot1 & PROT_WRITE))
mprotect(host_start, qemu_host_page_size, prot1 | PROT_WRITE);
/* read the corresponding file data */
if (pread(fd, g2h(start), end - start, offset) == -1)
return -1;
/* put final protection */
if (prot_new != (prot1 | PROT_WRITE))
mprotect(host_start, qemu_host_page_size, prot_new);
} else {
if (prot_new != prot1) {
mprotect(host_start, qemu_host_page_size, prot_new);
}
if (prot_new & PROT_WRITE) {
memset(g2h(start), 0, end - start);
}
}
return 0;
}
#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
#ifdef TARGET_AARCH64
# define TASK_UNMAPPED_BASE 0x5500000000
#else
# define TASK_UNMAPPED_BASE (1ul << 38)
#endif
#else
# define TASK_UNMAPPED_BASE 0x40000000
#endif
abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
unsigned long last_brk;
/* Subroutine of mmap_find_vma, used when we have pre-allocated a chunk
of guest address space. */
static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size,
abi_ulong align)
{
abi_ulong addr, end_addr, incr = qemu_host_page_size;
int prot;
bool looped = false;
if (size > reserved_va) {
return (abi_ulong)-1;
}
/* Note that start and size have already been aligned by mmap_find_vma. */
end_addr = start + size;
if (start > reserved_va - size) {
/* Start at the top of the address space. */
end_addr = ((reserved_va - size) & -align) + size;
looped = true;
}
/* Search downward from END_ADDR, checking to see if a page is in use. */
addr = end_addr;
while (1) {
addr -= incr;
if (addr > end_addr) {
if (looped) {
/* Failure. The entire address space has been searched. */
return (abi_ulong)-1;
}
/* Re-start at the top of the address space. */
addr = end_addr = ((reserved_va - size) & -align) + size;
looped = true;
} else {
prot = page_get_flags(addr);
if (prot) {
/* Page in use. Restart below this page. */
addr = end_addr = ((addr - size) & -align) + size;
} else if (addr && addr + size == end_addr) {
/* Success! All pages between ADDR and END_ADDR are free. */
if (start == mmap_next_start) {
mmap_next_start = addr;
}
return addr;
}
}
}
}
/*
* Find and reserve a free memory area of size 'size'. The search
* starts at 'start'.
* It must be called with mmap_lock() held.
* Return -1 if error.
*/
abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
{
void *ptr, *prev;
abi_ulong addr;
int wrapped, repeat;
align = MAX(align, qemu_host_page_size);
/* If 'start' == 0, then a default start address is used. */
if (start == 0) {
start = mmap_next_start;
} else {
start &= qemu_host_page_mask;
}
start = ROUND_UP(start, align);
size = HOST_PAGE_ALIGN(size);
if (reserved_va) {
return mmap_find_vma_reserved(start, size, align);
}
addr = start;
wrapped = repeat = 0;
prev = 0;
for (;; prev = ptr) {
/*
* Reserve needed memory area to avoid a race.
* It should be discarded using:
* - mmap() with MAP_FIXED flag
* - mremap() with MREMAP_FIXED flag
* - shmat() with SHM_REMAP flag
*/
ptr = mmap(g2h(addr), size, PROT_NONE,
MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, -1, 0);
/* ENOMEM, if host address space has no memory */
if (ptr == MAP_FAILED) {
return (abi_ulong)-1;
}
/* Count the number of sequential returns of the same address.
This is used to modify the search algorithm below. */
repeat = (ptr == prev ? repeat + 1 : 0);
if (h2g_valid(ptr + size - 1)) {
addr = h2g(ptr);
if ((addr & (align - 1)) == 0) {
/* Success. */
if (start == mmap_next_start && addr >= TASK_UNMAPPED_BASE) {
mmap_next_start = addr + size;
}
return addr;
}
/* The address is not properly aligned for the target. */
switch (repeat) {
case 0:
/* Assume the result that the kernel gave us is the
first with enough free space, so start again at the
next higher target page. */
addr = ROUND_UP(addr, align);
break;
case 1:
/* Sometimes the kernel decides to perform the allocation
at the top end of memory instead. */
addr &= -align;
break;
case 2:
/* Start over at low memory. */
addr = 0;
break;
default:
/* Fail. This unaligned block must the last. */
addr = -1;
break;
}
} else {
/* Since the result the kernel gave didn't fit, start
again at low memory. If any repetition, fail. */
addr = (repeat ? -1 : 0);
}
/* Unmap and try again. */
munmap(ptr, size);
/* ENOMEM if we checked the whole of the target address space. */
if (addr == (abi_ulong)-1) {
return (abi_ulong)-1;
} else if (addr == 0) {
if (wrapped) {
return (abi_ulong)-1;
}
wrapped = 1;
/* Don't actually use 0 when wrapping, instead indicate
that we'd truly like an allocation in low memory. */
addr = (mmap_min_addr > TARGET_PAGE_SIZE
? TARGET_PAGE_ALIGN(mmap_min_addr)
: TARGET_PAGE_SIZE);
} else if (wrapped && addr >= start) {
return (abi_ulong)-1;
}
}
}
/* NOTE: all the constants are the HOST ones */
abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
int flags, int fd, abi_ulong offset)
{
abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len;
int page_flags, host_prot;
mmap_lock();
trace_target_mmap(start, len, target_prot, flags, fd, offset);
if (!len) {
errno = EINVAL;
goto fail;
}
page_flags = validate_prot_to_pageflags(&host_prot, target_prot);
if (!page_flags) {
errno = EINVAL;
goto fail;
}
/* Also check for overflows... */
len = TARGET_PAGE_ALIGN(len);
if (!len) {
errno = ENOMEM;
goto fail;
}
if (offset & ~TARGET_PAGE_MASK) {
errno = EINVAL;
goto fail;
}
real_start = start & qemu_host_page_mask;
host_offset = offset & qemu_host_page_mask;
/* If the user is asking for the kernel to find a location, do that
before we truncate the length for mapping files below. */
if (!(flags & MAP_FIXED)) {
host_len = len + offset - host_offset;
host_len = HOST_PAGE_ALIGN(host_len);
start = mmap_find_vma(real_start, host_len, TARGET_PAGE_SIZE);
if (start == (abi_ulong)-1) {
errno = ENOMEM;
goto fail;
}
}
/* When mapping files into a memory area larger than the file, accesses
to pages beyond the file size will cause a SIGBUS.
For example, if mmaping a file of 100 bytes on a host with 4K pages
emulating a target with 8K pages, the target expects to be able to
access the first 8K. But the host will trap us on any access beyond
4K.
When emulating a target with a larger page-size than the hosts, we
may need to truncate file maps at EOF and add extra anonymous pages
up to the targets page boundary. */
if ((qemu_real_host_page_size < qemu_host_page_size) &&
!(flags & MAP_ANONYMOUS)) {
struct stat sb;
if (fstat (fd, &sb) == -1)
goto fail;
/* Are we trying to create a map beyond EOF?. */
if (offset + len > sb.st_size) {
/* If so, truncate the file map at eof aligned with
the hosts real pagesize. Additional anonymous maps
will be created beyond EOF. */
len = REAL_HOST_PAGE_ALIGN(sb.st_size - offset);
}
}
if (!(flags & MAP_FIXED)) {
unsigned long host_start;
void *p;
host_len = len + offset - host_offset;
host_len = HOST_PAGE_ALIGN(host_len);
/* Note: we prefer to control the mapping address. It is
especially important if qemu_host_page_size >
qemu_real_host_page_size */
p = mmap(g2h(start), host_len, host_prot,
flags | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
if (p == MAP_FAILED) {
goto fail;
}
/* update start so that it points to the file position at 'offset' */
host_start = (unsigned long)p;
if (!(flags & MAP_ANONYMOUS)) {
p = mmap(g2h(start), len, host_prot,
flags | MAP_FIXED, fd, host_offset);
if (p == MAP_FAILED) {
munmap(g2h(start), host_len);
goto fail;
}
host_start += offset - host_offset;
}
start = h2g(host_start);
} else {
if (start & ~TARGET_PAGE_MASK) {
errno = EINVAL;
goto fail;
}
end = start + len;
real_end = HOST_PAGE_ALIGN(end);
/*
* Test if requested memory area fits target address space
* It can fail only on 64-bit host with 32-bit target.
* On any other target/host host mmap() handles this error correctly.
*/
if (end < start || !guest_range_valid(start, len)) {
errno = ENOMEM;
goto fail;
}
/* worst case: we cannot map the file because the offset is not
aligned, so we read it */
if (!(flags & MAP_ANONYMOUS) &&
(offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) {
/* msync() won't work here, so we return an error if write is
possible while it is a shared mapping */
if ((flags & MAP_TYPE) == MAP_SHARED &&
(host_prot & PROT_WRITE)) {
errno = EINVAL;
goto fail;
}
retaddr = target_mmap(start, len, target_prot | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
if (retaddr == -1)
goto fail;
if (pread(fd, g2h(start), len, offset) == -1)
goto fail;
if (!(host_prot & PROT_WRITE)) {
ret = target_mprotect(start, len, target_prot);
assert(ret == 0);
}
goto the_end;
}
/* handle the start of the mapping */
if (start > real_start) {
if (real_end == real_start + qemu_host_page_size) {
/* one single host page */
ret = mmap_frag(real_start, start, end,
host_prot, flags, fd, offset);
if (ret == -1)
goto fail;
goto the_end1;
}
ret = mmap_frag(real_start, start, real_start + qemu_host_page_size,
host_prot, flags, fd, offset);
if (ret == -1)
goto fail;
real_start += qemu_host_page_size;
}
/* handle the end of the mapping */
if (end < real_end) {
ret = mmap_frag(real_end - qemu_host_page_size,
real_end - qemu_host_page_size, end,
host_prot, flags, fd,
offset + real_end - qemu_host_page_size - start);
if (ret == -1)
goto fail;
real_end -= qemu_host_page_size;
}
/* map the middle (easier) */
if (real_start < real_end) {
void *p;
unsigned long offset1;
if (flags & MAP_ANONYMOUS)
offset1 = 0;
else
offset1 = offset + real_start - start;
p = mmap(g2h(real_start), real_end - real_start,
host_prot, flags, fd, offset1);
if (p == MAP_FAILED)
goto fail;
}
}
the_end1:
if (flags & MAP_ANONYMOUS) {
page_flags |= PAGE_ANON;
}
page_flags |= PAGE_RESET;
page_set_flags(start, start + len, page_flags);
the_end:
trace_target_mmap_complete(start);
if (qemu_loglevel_mask(CPU_LOG_PAGE)) {
log_page_dump(__func__);
}
tb_invalidate_phys_range(start, start + len);
mmap_unlock();
return start;
fail:
mmap_unlock();
return -1;
}
static void mmap_reserve(abi_ulong start, abi_ulong size)
{
abi_ulong real_start;
abi_ulong real_end;
abi_ulong addr;
abi_ulong end;
int prot;
real_start = start & qemu_host_page_mask;
real_end = HOST_PAGE_ALIGN(start + size);
end = start + size;
if (start > real_start) {
/* handle host page containing start */
prot = 0;
for (addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
prot |= page_get_flags(addr);
}
if (real_end == real_start + qemu_host_page_size) {
for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
prot |= page_get_flags(addr);
}
end = real_end;
}
if (prot != 0)
real_start += qemu_host_page_size;
}
if (end < real_end) {
prot = 0;
for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
prot |= page_get_flags(addr);
}
if (prot != 0)
real_end -= qemu_host_page_size;
}
if (real_start != real_end) {
mmap(g2h(real_start), real_end - real_start, PROT_NONE,
MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE,
-1, 0);
}
}
int target_munmap(abi_ulong start, abi_ulong len)
{
abi_ulong end, real_start, real_end, addr;
int prot, ret;
trace_target_munmap(start, len);
if (start & ~TARGET_PAGE_MASK)
return -TARGET_EINVAL;
len = TARGET_PAGE_ALIGN(len);
if (len == 0 || !guest_range_valid(start, len)) {
return -TARGET_EINVAL;
}
mmap_lock();
end = start + len;
real_start = start & qemu_host_page_mask;
real_end = HOST_PAGE_ALIGN(end);
if (start > real_start) {
/* handle host page containing start */
prot = 0;
for(addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
prot |= page_get_flags(addr);
}
if (real_end == real_start + qemu_host_page_size) {
for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
prot |= page_get_flags(addr);
}
end = real_end;
}
if (prot != 0)
real_start += qemu_host_page_size;
}
if (end < real_end) {
prot = 0;
for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
prot |= page_get_flags(addr);
}
if (prot != 0)
real_end -= qemu_host_page_size;
}
ret = 0;
/* unmap what we can */
if (real_start < real_end) {
if (reserved_va) {
mmap_reserve(real_start, real_end - real_start);
} else {
ret = munmap(g2h(real_start), real_end - real_start);
}
}
if (ret == 0) {
page_set_flags(start, start + len, 0);
tb_invalidate_phys_range(start, start + len);
}
mmap_unlock();
return ret;
}
abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
abi_ulong new_size, unsigned long flags,
abi_ulong new_addr)
{
int prot;
void *host_addr;
if (!guest_range_valid(old_addr, old_size) ||
((flags & MREMAP_FIXED) &&
!guest_range_valid(new_addr, new_size)) ||
((flags & MREMAP_MAYMOVE) == 0 &&
!guest_range_valid(old_addr, new_size))) {
errno = ENOMEM;
return -1;
}
mmap_lock();
if (flags & MREMAP_FIXED) {
host_addr = mremap(g2h(old_addr), old_size, new_size,
flags, g2h(new_addr));
if (reserved_va && host_addr != MAP_FAILED) {
/* If new and old addresses overlap then the above mremap will
already have failed with EINVAL. */
mmap_reserve(old_addr, old_size);
}
} else if (flags & MREMAP_MAYMOVE) {
abi_ulong mmap_start;
mmap_start = mmap_find_vma(0, new_size, TARGET_PAGE_SIZE);
if (mmap_start == -1) {
errno = ENOMEM;
host_addr = MAP_FAILED;
} else {
host_addr = mremap(g2h(old_addr), old_size, new_size,
flags | MREMAP_FIXED, g2h(mmap_start));
if (reserved_va) {
mmap_reserve(old_addr, old_size);
}
}
} else {
int prot = 0;
if (reserved_va && old_size < new_size) {
abi_ulong addr;
for (addr = old_addr + old_size;
addr < old_addr + new_size;
addr++) {
prot |= page_get_flags(addr);
}
}
if (prot == 0) {
host_addr = mremap(g2h(old_addr), old_size, new_size, flags);
if (host_addr != MAP_FAILED) {
/* Check if address fits target address space */
if (!guest_range_valid(h2g(host_addr), new_size)) {
/* Revert mremap() changes */
host_addr = mremap(g2h(old_addr), new_size, old_size,
flags);
errno = ENOMEM;
host_addr = MAP_FAILED;
} else if (reserved_va && old_size > new_size) {
mmap_reserve(old_addr + old_size, old_size - new_size);
}
}
} else {
errno = ENOMEM;
host_addr = MAP_FAILED;
}
}
if (host_addr == MAP_FAILED) {
new_addr = -1;
} else {
new_addr = h2g(host_addr);
prot = page_get_flags(old_addr);
page_set_flags(old_addr, old_addr + old_size, 0);
page_set_flags(new_addr, new_addr + new_size,
prot | PAGE_VALID | PAGE_RESET);
}
tb_invalidate_phys_range(new_addr, new_addr + new_size);
mmap_unlock();
return new_addr;
}
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