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Subject[PATCH 3.2 070/104] kprobes/x86: Blacklist indirect thunk functions for kprobes
3.2.101-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@kernel.org>

commit c1804a236894ecc942da7dc6c5abe209e56cba93 upstream.

Mark __x86_indirect_thunk_* functions as blacklist for kprobes
because those functions can be called from anywhere in the kernel
including blacklist functions of kprobes.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Link: https://lkml.kernel.org/r/151629209111.10241.5444852823378068683.stgit@devbox
[bwh: Backported to 3.2: We don't have _ASM_NOKPROBE etc., so add indirect
thunks to the built-in blacklist]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -53,6 +53,9 @@
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <asm/uaccess.h>
+#ifdef CONFIG_RETPOLINE
+#include <asm/nospec-branch.h>
+#endif

#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
@@ -99,6 +102,11 @@ static struct kprobe_blackpoint kprobe_b
{"irq_entries_start",},
{"common_interrupt",},
{"mcount",}, /* mcount can be called from everywhere */
+#ifdef CONFIG_RETPOLINE
+ {"__indirect_thunk_start",
+ /* Linker scripts can't set symbol sizes */
+ .range = (size_t)__indirect_thunk_size},
+#endif
{NULL} /* Terminator */
};

@@ -1986,7 +1994,7 @@ static int __init init_kprobes(void)
&size, &offset, &modname, namebuf);
if (!symbol_name)
kb->range = 0;
- else
+ else if (size)
kb->range = size;
}

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -173,6 +173,7 @@ enum spectre_v2_mitigation {

extern char __indirect_thunk_start[];
extern char __indirect_thunk_end[];
+extern char __indirect_thunk_size[];

/*
* On VMEXIT we must ensure that no RSB predictions learned in the guest
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -112,6 +112,7 @@ SECTIONS
__indirect_thunk_start = .;
*(.text.__x86.indirect_thunk)
__indirect_thunk_end = .;
+ __indirect_thunk_size = __indirect_thunk_end - __indirect_thunk_start;
#endif

/* End of text section */
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