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Avoid assertions when testing arm64 cow bug. (#8405)

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At least in one case the arm64 cow kernel bug test triggers an assert, which is a problem because it cannot be ignored like cases where the bug is found.

On older systems (Linux <4.5) madvise fails because MADV_FREE is not supported. We treat these failures as an indication the system is not affected.

Fixes #8351, #8406
This commit is contained in:
Yossi Gottlieb 2021-01-28 10:33:45 +02:00 committed by GitHub
parent 0367a80819
commit 3a5049042a
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 68 additions and 33 deletions
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101
src/server.c
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@ -5200,7 +5200,7 @@ static int smapsGetSharedDirty(unsigned long addr) {
FILE *f;
f = fopen("/proc/self/smaps", "r");
serverAssert(f);
if (!f) return -1;
while (1) {
if (!fgets(buf, sizeof(buf), f))
@ -5211,8 +5211,8 @@ static int smapsGetSharedDirty(unsigned long addr) {
in_mapping = from <= addr && addr < to;
if (in_mapping && !memcmp(buf, "Shared_Dirty:", 13)) {
ret = sscanf(buf, "%*s %d", &val);
serverAssert(ret == 1);
sscanf(buf, "%*s %d", &val);
/* If parsing fails, we remain with val == -1 */
break;
}
}
@ -5226,23 +5226,33 @@ static int smapsGetSharedDirty(unsigned long addr) {
* kernel is affected.
* The bug was fixed in commit ff1712f953e27f0b0718762ec17d0adb15c9fd0b
* titled: "arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect()"
* Return 1 if the kernel seems to be affected, and 0 otherwise. */
* Return -1 on unexpected test failure, 1 if the kernel seems to be affected,
* and 0 otherwise. */
int linuxMadvFreeForkBugCheck(void) {
int ret, pipefd[2];
int ret, pipefd[2] = { -1, -1 };
pid_t pid;
char *p, *q, bug_found = 0;
const long map_size = 3 * 4096;
char *p = NULL, *q;
int bug_found = 0;
long page_size = sysconf(_SC_PAGESIZE);
long map_size = 3 * page_size;
/* Create a memory map that's in our full control (not one used by the allocator). */
p = mmap(NULL, map_size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
serverAssert(p != MAP_FAILED);
if (p == MAP_FAILED) {
serverLog(LL_WARNING, "Failed to mmap(): %s", strerror(errno));
return -1;
}
q = p + 4096;
q = p + page_size;
/* Split the memory map in 3 pages by setting their protection as RO|RW|RO to prevent
* Linux from merging this memory map with adjacent VMAs. */
ret = mprotect(q, 4096, PROT_READ | PROT_WRITE);
serverAssert(!ret);
ret = mprotect(q, page_size, PROT_READ | PROT_WRITE);
if (ret < 0) {
serverLog(LL_WARNING, "Failed to mprotect(): %s", strerror(errno));
bug_found = -1;
goto exit;
}
/* Write to the page once to make it resident */
*(volatile char*)q = 0;
@ -5251,8 +5261,16 @@ int linuxMadvFreeForkBugCheck(void) {
#ifndef MADV_FREE
#define MADV_FREE 8
#endif
ret = madvise(q, 4096, MADV_FREE);
serverAssert(!ret);
ret = madvise(q, page_size, MADV_FREE);
if (ret < 0) {
/* MADV_FREE is not available on older kernels that are presumably
* not affected. */
if (errno == EINVAL) goto exit;
serverLog(LL_WARNING, "Failed to madvise(): %s", strerror(errno));
bug_found = -1;
goto exit;
}
/* Write to the page after being marked for freeing, this is supposed to take
* ownership of that page again. */
@ -5260,37 +5278,47 @@ int linuxMadvFreeForkBugCheck(void) {
/* Create a pipe for the child to return the info to the parent. */
ret = pipe(pipefd);
serverAssert(!ret);
if (ret < 0) {
serverLog(LL_WARNING, "Failed to create pipe: %s", strerror(errno));
bug_found = -1;
goto exit;
}
/* Fork the process. */
pid = fork();
serverAssert(pid >= 0);
if (!pid) {
/* Child: check if the page is marked as dirty, expecing 4 (kB).
if (pid < 0) {
serverLog(LL_WARNING, "Failed to fork: %s", strerror(errno));
bug_found = -1;
goto exit;
} else if (!pid) {
/* Child: check if the page is marked as dirty, page_size in kb.
* A value of 0 means the kernel is affected by the bug. */
if (!smapsGetSharedDirty((unsigned long)q))
ret = smapsGetSharedDirty((unsigned long) q);
if (!ret)
bug_found = 1;
else if (ret == -1) /* Failed to read */
bug_found = -1;
ret = write(pipefd[1], &bug_found, 1);
serverAssert(ret == 1);
if (write(pipefd[1], &bug_found, sizeof(bug_found)) < 0)
serverLog(LL_WARNING, "Failed to write to parent: %s", strerror(errno));
exit(0);
} else {
/* Read the result from the child. */
ret = read(pipefd[0], &bug_found, 1);
serverAssert(ret == 1);
ret = read(pipefd[0], &bug_found, sizeof(bug_found));
if (ret < 0) {
serverLog(LL_WARNING, "Failed to read from child: %s", strerror(errno));
bug_found = -1;
}
/* Reap the child pid. */
serverAssert(waitpid(pid, NULL, 0) == pid);
waitpid(pid, NULL, 0);
}
exit:
/* Cleanup */
ret = close(pipefd[0]);
serverAssert(!ret);
ret = close(pipefd[1]);
serverAssert(!ret);
ret = munmap(p, map_size);
serverAssert(!ret);
if (pipefd[0] != -1) close(pipefd[0]);
if (pipefd[1] != -1) close(pipefd[1]);
if (p != NULL) munmap(p, map_size);
return bug_found;
}
@ -5901,10 +5929,17 @@ int main(int argc, char **argv) {
#ifdef __linux__
linuxMemoryWarnings();
#if defined (__arm64__)
if (linuxMadvFreeForkBugCheck()) {
serverLog(LL_WARNING,"WARNING Your kernel has a bug that could lead to data corruption during background save. Please upgrade to the latest stable kernel.");
int ret;
if ((ret = linuxMadvFreeForkBugCheck())) {
if (ret == 1)
serverLog(LL_WARNING,"WARNING Your kernel has a bug that could lead to data corruption during background save. "
"Please upgrade to the latest stable kernel.");
else
serverLog(LL_WARNING, "Failed to test the kernel for a bug that could lead to data corruption during background save. "
"Your system could be affected, please report this error.");
if (!checkIgnoreWarning("ARM64-COW-BUG")) {
serverLog(LL_WARNING,"Redis will now exit to prevent data corruption. Note that it is possible to suppress this warning by setting the following config: ignore-warnings ARM64-COW-BUG");
serverLog(LL_WARNING,"Redis will now exit to prevent data corruption. "
"Note that it is possible to suppress this warning by setting the following config: ignore-warnings ARM64-COW-BUG");
exit(1);
}
}