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tcg: Merge buffer protection and guard page protection

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Do not handle protections on a case-by-case basis in the
various alloc_code_gen_buffer instances; do it within a
single loop in tcg_region_init.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2021-03-10 17:27:49 -06:00
parent ba22783d6e
commit 22c6a9938f
1 changed files with 31 additions and 14 deletions
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45
tcg/region.c
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@ -535,11 +535,6 @@ static int alloc_code_gen_buffer(size_t tb_size, int splitwx, Error **errp)
}
#endif
if (qemu_mprotect_rwx(buf, size)) {
error_setg_errno(errp, errno, "mprotect of jit buffer");
return false;
}
region.start_aligned = buf;
region.total_size = size;
@ -823,8 +818,7 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
{
const size_t page_size = qemu_real_host_page_size;
size_t region_size;
size_t i;
int have_prot;
int have_prot, need_prot;
/* Size the buffer. */
if (tb_size == 0) {
@ -884,18 +878,41 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
* Set guard pages in the rw buffer, as that's the one into which
* buffer overruns could occur. Do not set guard pages in the rx
* buffer -- let that one use hugepages throughout.
* Work with the page protections set up with the initial mapping.
*/
for (i = 0; i < region.n; i++) {
need_prot = PAGE_READ | PAGE_WRITE;
#ifndef CONFIG_TCG_INTERPRETER
if (tcg_splitwx_diff == 0) {
need_prot |= PAGE_EXEC;
}
#endif
for (size_t i = 0, n = region.n; i < n; i++) {
void *start, *end;
tcg_region_bounds(i, &start, &end);
if (have_prot != need_prot) {
int rc;
/*
* macOS 11.2 has a bug (Apple Feedback FB8994773) in which mprotect
* rejects a permission change from RWX -> NONE. Guard pages are
* nice for bug detection but are not essential; ignore any failure.
*/
(void)qemu_mprotect_none(end, page_size);
if (need_prot == (PAGE_READ | PAGE_WRITE | PAGE_EXEC)) {
rc = qemu_mprotect_rwx(start, end - start);
} else if (need_prot == (PAGE_READ | PAGE_WRITE)) {
rc = qemu_mprotect_rw(start, end - start);
} else {
g_assert_not_reached();
}
if (rc) {
error_setg_errno(&error_fatal, errno,
"mprotect of jit buffer");
}
}
if (have_prot != 0) {
/*
* macOS 11.2 has a bug (Apple Feedback FB8994773) in which mprotect
* rejects a permission change from RWX -> NONE. Guard pages are
* nice for bug detection but are not essential; ignore any failure.
*/
(void)qemu_mprotect_none(end, page_size);
}
}
tcg_region_trees_init();