From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- tools/objtool/signal.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 tools/objtool/signal.c (limited to 'tools/objtool/signal.c') diff --git a/tools/objtool/signal.c b/tools/objtool/signal.c new file mode 100644 index 000000000..af5c65c0f --- /dev/null +++ b/tools/objtool/signal.c @@ -0,0 +1,135 @@ +/* + * signal.c: Register a sigaltstack for objtool, to be able to + * run a signal handler on a separate stack even if + * the main process stack has overflown. Print out + * stack overflow errors when this happens. + */ +#include +#include +#include +#include +#include +#include + +#include +#include + +static unsigned long stack_limit; + +static bool is_stack_overflow(void *fault_addr) +{ + unsigned long fault = (unsigned long)fault_addr; + + /* Check if fault is in the guard page just below the limit. */ + return fault < stack_limit && fault >= stack_limit - 4096; +} + +static void signal_handler(int sig_num, siginfo_t *info, void *context) +{ + struct sigaction sa_dfl = {0}; + const char *sig_name; + char msg[256]; + int msg_len; + + switch (sig_num) { + case SIGSEGV: sig_name = "SIGSEGV"; break; + case SIGBUS: sig_name = "SIGBUS"; break; + case SIGILL: sig_name = "SIGILL"; break; + case SIGABRT: sig_name = "SIGABRT"; break; + default: sig_name = "Unknown signal"; break; + } + + if (is_stack_overflow(info->si_addr)) { + msg_len = snprintf(msg, sizeof(msg), + "%s: error: %s: objtool stack overflow!\n", + objname, sig_name); + } else { + msg_len = snprintf(msg, sizeof(msg), + "%s: error: %s: objtool crash!\n", + objname, sig_name); + } + + msg_len = write(STDERR_FILENO, msg, msg_len); + + /* Re-raise the signal to trigger the core dump */ + sa_dfl.sa_handler = SIG_DFL; + sigaction(sig_num, &sa_dfl, NULL); + raise(sig_num); +} + +static int read_stack_limit(void) +{ + unsigned long stack_start, stack_end; + struct rlimit rlim; + char line[256]; + int ret = 0; + FILE *fp; + + if (getrlimit(RLIMIT_STACK, &rlim)) { + ERROR_GLIBC("getrlimit"); + return -1; + } + + fp = fopen("/proc/self/maps", "r"); + if (!fp) { + ERROR_GLIBC("fopen"); + return -1; + } + + while (fgets(line, sizeof(line), fp)) { + if (strstr(line, "[stack]")) { + if (sscanf(line, "%lx-%lx", &stack_start, &stack_end) != 2) { + ERROR_GLIBC("sscanf"); + ret = -1; + goto done; + } + stack_limit = stack_end - rlim.rlim_cur; + goto done; + } + } + + ret = -1; + ERROR("/proc/self/maps: can't find [stack]"); + +done: + fclose(fp); + + return ret; +} + +int init_signal_handler(void) +{ + int signals[] = {SIGSEGV, SIGBUS, SIGILL, SIGABRT}; + struct sigaction sa; + stack_t ss; + + if (read_stack_limit()) + return -1; + + ss.ss_sp = malloc(SIGSTKSZ); + if (!ss.ss_sp) { + ERROR_GLIBC("malloc"); + return -1; + } + ss.ss_size = SIGSTKSZ; + ss.ss_flags = 0; + + if (sigaltstack(&ss, NULL) == -1) { + ERROR_GLIBC("sigaltstack"); + return -1; + } + + sa.sa_sigaction = signal_handler; + sigemptyset(&sa.sa_mask); + + sa.sa_flags = SA_ONSTACK | SA_SIGINFO; + + for (int i = 0; i < ARRAY_SIZE(signals); i++) { + if (sigaction(signals[i], &sa, NULL) == -1) { + ERROR_GLIBC("sigaction"); + return -1; + } + } + + return 0; +} -- cgit v1.3.1