[GIT PULL] x86 fixes

Ingo Molnar
2020-07-25T11:46:46Z

Linus,

Please pull the latest x86/urgent git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-urgent-2020-07-25

# HEAD: d181d2da0141371bbc360eaea78719203e165e1c x86/dumpstack: Dump user space code correctly again

Misc fixes:

- Fix a section end page alignment assumption that was causing crashes

- Fix ORC unwinding on freshly forked tasks which haven't executed yet
and which have empty user task stacks

- Fix the debug.exception-trace=1 sysctl dumping of user stacks, which
was broken by recent maccess changes

out-of-topic modifications in x86-urgent-2020-07-25:
------------------------------------------------------
include/asm-generic/vmlinux.lds.h # de2b41be8fcc: x86, vmlinux.lds: Page-align

Thanks,

Ingo

------------------>
Joerg Roedel (1):
x86, vmlinux.lds: Page-align end of ..page_aligned sections

Josh Poimboeuf (2):
x86/unwind/orc: Fix ORC for newly forked tasks
x86/stacktrace: Fix reliable check for empty user task stacks

Thomas Gleixner (1):
x86/dumpstack: Dump user space code correctly again

arch/x86/kernel/dumpstack.c | 27 +++++++++++++++++----------
arch/x86/kernel/stacktrace.c | 5 -----
arch/x86/kernel/unwind_orc.c | 8 ++++++--
arch/x86/kernel/vmlinux.lds.S | 1 +
include/asm-generic/vmlinux.lds.h | 5 ++++-
5 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index b037cfa7c0c5..7401cc12c3cc 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -71,6 +71,22 @@ static void printk_stack_address(unsigned long address, int reliable,
printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
}

+static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src,
+ unsigned int nbytes)
+{
+ if (!user_mode(regs))
+ return copy_from_kernel_nofault(buf, (u8 *)src, nbytes);
+
+ /*
+ * Make sure userspace isn't trying to trick us into dumping kernel
+ * memory by pointing the userspace instruction pointer at it.
+ */
+ if (__chk_range_not_ok(src, nbytes, TASK_SIZE_MAX))
+ return -EINVAL;
+
+ return copy_from_user_nmi(buf, (void __user *)src, nbytes);
+}
+
/*
* There are a couple of reasons for the 2/3rd prologue, courtesy of Linus:
*
@@ -97,17 +113,8 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
u8 opcodes[OPCODE_BUFSIZE];
unsigned long prologue = regs->ip - PROLOGUE_SIZE;
- bool bad_ip;
-
- /*
- * Make sure userspace isn't trying to trick us into dumping kernel
- * memory by pointing the userspace instruction pointer at it.
- */
- bad_ip = user_mode(regs) &&
- __chk_range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);

- if (bad_ip || copy_from_kernel_nofault(opcodes, (u8 *)prologue,
- OPCODE_BUFSIZE)) {
+ if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
printk("%sCode: Bad RIP value.\n", loglvl);
} else {
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 6ad43fc44556..2fd698e28e4d 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -58,7 +58,6 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
* or a page fault), which can make frame pointers
* unreliable.
*/
-
if (IS_ENABLED(CONFIG_FRAME_POINTER))
return -EINVAL;
}
@@ -81,10 +80,6 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
if (unwind_error(&state))
return -EINVAL;

- /* Success path for non-user tasks, i.e. kthreads and idle tasks */
- if (!(task->flags & (PF_KTHREAD | PF_IDLE)))
- return -EINVAL;
-
return 0;
}

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 7f969b2d240f..ec88bbe08a32 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -440,8 +440,11 @@ bool unwind_next_frame(struct unwind_state *state)
/*
* Find the orc_entry associated with the text address.
*
- * Decrement call return addresses by one so they work for sibling
- * calls and calls to noreturn functions.
+ * For a call frame (as opposed to a signal frame), state->ip points to
+ * the instruction after the call. That instruction's stack layout
+ * could be different from the call instruction's layout, for example
+ * if the call was to a noreturn function. So get the ORC data for the
+ * call instruction itself.
*/
orc = orc_find(state->signal ? state->ip : state->ip - 1);
if (!orc) {
@@ -662,6 +665,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
state->sp = task->thread.sp;
state->bp = READ_ONCE_NOCHECK(frame->bp);
state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
+ state->signal = (void *)state->ip == ret_from_fork;
}

if (get_stack_info((unsigned long *)state->sp, state->task,
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3bfc8dd8a43d..9a03e5b23135 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -358,6 +358,7 @@ SECTIONS
.bss : AT(ADDR(.bss) - LOAD_OFFSET) {
__bss_start = .;
*(.bss..page_aligned)
+ . = ALIGN(PAGE_SIZE);
*(BSS_MAIN)
BSS_DECRYPTED
. = ALIGN(PAGE_SIZE);
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index db600ef218d7..052e0f05a984 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -341,7 +341,8 @@

#define PAGE_ALIGNED_DATA(page_align) \
. = ALIGN(page_align); \
- *(.data..page_aligned)
+ *(.data..page_aligned) \
+ . = ALIGN(page_align);

#define READ_MOSTLY_DATA(align) \
. = ALIGN(align); \
@@ -737,7 +738,9 @@
. = ALIGN(bss_align); \
.bss : AT(ADDR(.bss) - LOAD_OFFSET) { \
BSS_FIRST_SECTIONS \
+ . = ALIGN(PAGE_SIZE); \
*(.bss..page_aligned) \
+ . = ALIGN(PAGE_SIZE); \
*(.dynbss) \
*(BSS_MAIN) \
*(COMMON) \