@@ -320,10 +320,13 @@ The size of the structure is 64 bytes on 64-bit hypervisors. It will be
* `new_addr` is the address of the function that is replacing the old
function. The address is filled in during relocation. The value **MUST** be
- the address of the new function in the file.
+ either the address of the new function in the file, or zero if we are NOPing out
+ at `old_addr` (and `new_size` **MUST** not be zero).
* `old_size` and `new_size` contain the sizes of the respective functions in bytes.
- The value of `old_size` **MUST** not be zero.
+ The value of `old_size` **MUST** not be zero. If the value of `new_addr` is
+ zero then `new_size` determines how many instruction bytes to NOP (up to
+ opaque size modulo smallest platform instruction - 1 byte x86 and 4 bytes on ARM).
* `version` is to be one.
@@ -101,7 +101,7 @@ static void __init arch_init_ideal_nops(void)
}
/* Use this to add nops to a buffer, then text_poke the whole buffer. */
-static void init_or_livepatch add_nops(void *insns, unsigned int len)
+void init_or_livepatch add_nops(void *insns, unsigned int len)
{
while ( len > 0 )
{
@@ -12,8 +12,7 @@
#include <xen/livepatch.h>
#include <asm/nmi.h>
-
-#define PATCH_INSN_SIZE 5
+#include <asm/livepatch.h>
int arch_livepatch_quiesce(void)
{
@@ -31,8 +30,8 @@ void arch_livepatch_revive(void)
int arch_livepatch_verify_func(const struct livepatch_func *func)
{
- /* No NOP patching yet. */
- if ( !func->new_size )
+ /* If NOPing only do up to maximum amount we can put in the ->opaque. */
+ if ( !func->new_addr && func->new_size > sizeof(func->opaque) )
return -EOPNOTSUPP;
if ( func->old_size < PATCH_INSN_SIZE )
@@ -43,23 +42,36 @@ int arch_livepatch_verify_func(const struct livepatch_func *func)
void arch_livepatch_apply_jmp(struct livepatch_func *func)
{
- int32_t val;
uint8_t *old_ptr;
-
- BUILD_BUG_ON(PATCH_INSN_SIZE > sizeof(func->opaque));
- BUILD_BUG_ON(PATCH_INSN_SIZE != (1 + sizeof(val)));
+ uint8_t insn[sizeof(func->opaque)];
+ size_t len;
old_ptr = func->old_addr;
- memcpy(func->opaque, old_ptr, PATCH_INSN_SIZE);
+ len = arch_livepatch_insn_len(func);
+ if ( !len )
+ return;
+
+ memcpy(func->opaque, old_ptr, len);
+ if ( func->new_addr )
+ {
+ int32_t val;
+
+ BUILD_BUG_ON(PATCH_INSN_SIZE != (1 + sizeof(val)));
+
+ insn[0] = 0xe9;
+ val = func->new_addr - func->old_addr - PATCH_INSN_SIZE;
+
+ memcpy(&insn[1], &val, sizeof(val));
+ }
+ else
+ add_nops(&insn, len);
- *old_ptr++ = 0xe9; /* Relative jump */
- val = func->new_addr - func->old_addr - PATCH_INSN_SIZE;
- memcpy(old_ptr, &val, sizeof(val));
+ memcpy(old_ptr, insn, len);
}
void arch_livepatch_revert_jmp(const struct livepatch_func *func)
{
- memcpy(func->old_addr, func->opaque, PATCH_INSN_SIZE);
+ memcpy(func->old_addr, func->opaque, arch_livepatch_insn_len(func));
}
/* Serialise the CPU pipeline. */
@@ -510,7 +510,8 @@ static int prepare_payload(struct payload *payload,
return -EOPNOTSUPP;
}
- if ( !f->new_addr || !f->new_size )
+ /* 'old_addr', 'new_addr', 'new_size' can all be zero. */
+ if ( !f->old_size )
{
dprintk(XENLOG_ERR, LIVEPATCH "%s: Address or size fields are zero!\n",
elf->name);
@@ -27,6 +27,7 @@ struct alt_instr {
#define ALT_ORIG_PTR(a) __ALT_PTR(a, instr_offset)
#define ALT_REPL_PTR(a) __ALT_PTR(a, repl_offset)
+extern void add_nops(void *insns, unsigned int len);
/* Similar to alternative_instructions except it can be run with IRQs enabled. */
extern void apply_alternatives(const struct alt_instr *start,
const struct alt_instr *end);
new file mode 100644
@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2016 Oracle and/or its affiliates. All rights reserved.
+ *
+ */
+
+#ifndef __XEN_X86_LIVEPATCH_H__
+#define __XEN_X86_LIVEPATCH_H__
+
+#define PATCH_INSN_SIZE 5
+
+#endif /* __XEN_X86_LIVEPATCH_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
@@ -66,7 +66,16 @@ int arch_livepatch_secure(const void *va, unsigned int pages, enum va_type types
void arch_livepatch_init(void);
#include <public/sysctl.h> /* For struct livepatch_func. */
+#include <asm/livepatch.h> /* For PATCH_INSN_SIZE. */
int arch_livepatch_verify_func(const struct livepatch_func *func);
+
+static inline size_t arch_livepatch_insn_len(const struct livepatch_func *func)
+{
+ if ( !func->new_addr )
+ return func->new_size;
+
+ return PATCH_INSN_SIZE;
+}
/*
* These functions are called around the critical region patching live code,
* for an architecture to take make appropratie global state adjustments.
The NOP functionality will NOP any of the code at the 'old_addr' or at 'name' if the 'new_addr' is zero. The purpose of this is to NOP out calls, such as: e8 <4-bytes-offset> (5 byte insn), or on ARM a 4 byte insn for branching. We need the EIP of where we need to the NOP, and that can be provided via the `old_addr` or `name`. If the `old_addr` is provided we will NOP 'new_size' amount of bytes at that location. The amount is up to 31 instructions if desired (which is the size of the opaque member). If there is a need to NOP more then either more 'struct livepatch_func' structures need to be present or we have to implement a variable size buffer. While at it, also unify the code on x86 patching so it is a bit simpler (instead of two seperate writes just make it one memcpy). Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> --- Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Ross Lagerwall <ross.lagerwall@citrix.com> Cc: Jan Beulich <jbeulich@suse.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> v3: First submission v4: Fix description - e9 -> e8 Remove the restriction of only doing 5 or 4 bytes. Redo the patching code to deal with variable size of new_size. Expand the amount of bytes we can NOP. Move the PATCH_INSN_SIZE definition in platform specific headers Move the get_len to livepatch_get_insn_len inline function. --- docs/misc/livepatch.markdown | 7 +++++-- xen/arch/x86/alternative.c | 2 +- xen/arch/x86/livepatch.c | 38 +++++++++++++++++++++++++------------- xen/common/livepatch.c | 3 ++- xen/include/asm-x86/alternative.h | 1 + xen/include/asm-x86/livepatch.h | 21 +++++++++++++++++++++ xen/include/xen/livepatch.h | 9 +++++++++ 7 files changed, 64 insertions(+), 17 deletions(-) create mode 100644 xen/include/asm-x86/livepatch.h