Merge tag 'x86_fsgsbase_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git...

Pull x86 fsgsbase updates from Borislav Petkov:
 "Misc minor cleanups and corrections to the fsgsbase code and
  respective selftests"

* tag 'x86_fsgsbase_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests/x86/fsgsbase: Test PTRACE_PEEKUSER for GSBASE with invalid LDT GS
  selftests/x86/fsgsbase: Reap a forgotten child
  x86/fsgsbase: Replace static_cpu_has() with boot_cpu_has()
  x86/entry/64: Correct the comment over SAVE_AND_SET_GSBASE

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d977079a7d02e2b92d85d3b9c7545a8969d29d5e..748c2db3c54e777056a73b6876787e74bce0848b 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -842,8 +842,9 @@ SYM_CODE_START_LOCAL(paranoid_entry)
         * retrieve and set the current CPUs kernel GSBASE. The stored value
         * has to be restored in paranoid_exit unconditionally.
         *
-        * The MSR write ensures that no subsequent load is based on a
-        * mispredicted GSBASE. No extra FENCE required.
+        * The unconditional write to GS base below ensures that no subsequent
+        * loads based on a mispredicted GS base can happen, therefore no LFENCE
+        * is needed here.
         */
        SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx
        ret

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
index d552646411a9d5176737ea54a91530cb98d822dc..35cff5f2becf6bcbbdc34a890f29d3ba197e100d 100644 (file)
--- a/arch/x86/include/asm/fsgsbase.h
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -57,7 +57,7 @@ static inline unsigned long x86_fsbase_read_cpu(void)
 {
        unsigned long fsbase;
 
-       if (static_cpu_has(X86_FEATURE_FSGSBASE))
+       if (boot_cpu_has(X86_FEATURE_FSGSBASE))
                fsbase = rdfsbase();
        else
                rdmsrl(MSR_FS_BASE, fsbase);
@@ -67,7 +67,7 @@ static inline unsigned long x86_fsbase_read_cpu(void)
 
 static inline void x86_fsbase_write_cpu(unsigned long fsbase)
 {
-       if (static_cpu_has(X86_FEATURE_FSGSBASE))
+       if (boot_cpu_has(X86_FEATURE_FSGSBASE))
                wrfsbase(fsbase);
        else
                wrmsrl(MSR_FS_BASE, fsbase);

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9afefe325acb1f0425ef9f2bf12451fbc778b7bc..df342bedea88afc1e8571d6e20024bf477569c82 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -407,7 +407,7 @@ unsigned long x86_gsbase_read_cpu_inactive(void)
 {
        unsigned long gsbase;
 
-       if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
+       if (boot_cpu_has(X86_FEATURE_FSGSBASE)) {
                unsigned long flags;
 
                local_irq_save(flags);
@@ -422,7 +422,7 @@ unsigned long x86_gsbase_read_cpu_inactive(void)
 
 void x86_gsbase_write_cpu_inactive(unsigned long gsbase)
 {
-       if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
+       if (boot_cpu_has(X86_FEATURE_FSGSBASE)) {
                unsigned long flags;
 
                local_irq_save(flags);
@@ -439,7 +439,7 @@ unsigned long x86_fsbase_read_task(struct task_struct *task)
 
        if (task == current)
                fsbase = x86_fsbase_read_cpu();
-       else if (static_cpu_has(X86_FEATURE_FSGSBASE) ||
+       else if (boot_cpu_has(X86_FEATURE_FSGSBASE) ||
                 (task->thread.fsindex == 0))
                fsbase = task->thread.fsbase;
        else
@@ -454,7 +454,7 @@ unsigned long x86_gsbase_read_task(struct task_struct *task)
 
        if (task == current)
                gsbase = x86_gsbase_read_cpu_inactive();
-       else if (static_cpu_has(X86_FEATURE_FSGSBASE) ||
+       else if (boot_cpu_has(X86_FEATURE_FSGSBASE) ||
                 (task->thread.gsindex == 0))
                gsbase = task->thread.gsbase;
        else

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 9983195535237214f5085cc212f38592f109cc6a..7161cfc2e60b4e92c85fe0e97e95f7f3e668c1c1 100644 (file)
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -443,6 +443,68 @@ static void test_unexpected_base(void)
 
 #define USER_REGS_OFFSET(r) offsetof(struct user_regs_struct, r)
 
+static void test_ptrace_write_gs_read_base(void)
+{
+       int status;
+       pid_t child = fork();
+
+       if (child < 0)
+               err(1, "fork");
+
+       if (child == 0) {
+               printf("[RUN]\tPTRACE_POKE GS, read GSBASE back\n");
+
+               printf("[RUN]\tARCH_SET_GS to 1\n");
+               if (syscall(SYS_arch_prctl, ARCH_SET_GS, 1) != 0)
+                       err(1, "ARCH_SET_GS");
+
+               if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) != 0)
+                       err(1, "PTRACE_TRACEME");
+
+               raise(SIGTRAP);
+               _exit(0);
+       }
+
+       wait(&status);
+
+       if (WSTOPSIG(status) == SIGTRAP) {
+               unsigned long base;
+               unsigned long gs_offset = USER_REGS_OFFSET(gs);
+               unsigned long base_offset = USER_REGS_OFFSET(gs_base);
+
+               /* Read the initial base.  It should be 1. */
+               base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);
+               if (base == 1) {
+                       printf("[OK]\tGSBASE started at 1\n");
+               } else {
+                       nerrs++;
+                       printf("[FAIL]\tGSBASE started at 0x%lx\n", base);
+               }
+
+               printf("[RUN]\tSet GS = 0x7, read GSBASE\n");
+
+               /* Poke an LDT selector into GS. */
+               if (ptrace(PTRACE_POKEUSER, child, gs_offset, 0x7) != 0)
+                       err(1, "PTRACE_POKEUSER");
+
+               /* And read the base. */
+               base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);
+
+               if (base == 0 || base == 1) {
+                       printf("[OK]\tGSBASE reads as 0x%lx with invalid GS\n", base);
+               } else {
+                       nerrs++;
+                       printf("[FAIL]\tGSBASE=0x%lx (should be 0 or 1)\n", base);
+               }
+       }
+
+       ptrace(PTRACE_CONT, child, NULL, NULL);
+
+       wait(&status);
+       if (!WIFEXITED(status))
+               printf("[WARN]\tChild didn't exit cleanly.\n");
+}
+
 static void test_ptrace_write_gsbase(void)
 {
        int status;
@@ -517,6 +579,9 @@ static void test_ptrace_write_gsbase(void)
 
 END:
        ptrace(PTRACE_CONT, child, NULL, NULL);
+       wait(&status);
+       if (!WIFEXITED(status))
+               printf("[WARN]\tChild didn't exit cleanly.\n");
 }
 
 int main()
@@ -526,6 +591,9 @@ int main()
        shared_scratch = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
                              MAP_ANONYMOUS | MAP_SHARED, -1, 0);
 
+       /* Do these tests before we have an LDT. */
+       test_ptrace_write_gs_read_base();
+
        /* Probe FSGSBASE */
        sethandler(SIGILL, sigill, 0);
        if (sigsetjmp(jmpbuf, 1) == 0) {