summaryrefslogtreecommitdiff
path: root/arch/x86/kernel
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2024-05-14 08:51:37 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2024-05-14 08:51:37 -0700
commit25c7cb05fa61078d99d56fda36bd6d0a1638139d (patch)
tree509316274d6f4e4cac2b0121a631bfdd79ba2d2a /arch/x86/kernel
parentb4864f6565ab57d6418ec469330e320f77eeee95 (diff)
parent8dc8b02d707ee4167fffaf3a97003bcdac282876 (diff)
Merge tag 'x86_alternatives_for_v6.10_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 asm alternatives updates from Borislav Petkov: - Switch the in-place instruction patching which lead to at least one weird bug with 32-bit guests, seeing stale instruction bytes, to one working on a buffer, like the rest of the alternatives code does - Add a long overdue check to the X86_FEATURE flag modifying functions to warn when former get changed in a non-compatible way after alternatives have been patched because those changes will be already wrong - Other cleanups * tag 'x86_alternatives_for_v6.10_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/alternatives: Remove alternative_input_2() x86/alternatives: Sort local vars in apply_alternatives() x86/alternatives: Optimize optimize_nops() x86/alternatives: Get rid of __optimize_nops() x86/alternatives: Use a temporary buffer when optimizing NOPs x86/alternatives: Catch late X86_FEATURE modifiers
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r--arch/x86/kernel/alternative.c133
-rw-r--r--arch/x86/kernel/callthunks.c9
-rw-r--r--arch/x86/kernel/cpu/cpuid-deps.c3
3 files changed, 64 insertions, 81 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 45a280f2161c..7555c15b7183 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -125,6 +125,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
};
/*
+ * Nomenclature for variable names to simplify and clarify this code and ease
+ * any potential staring at it:
+ *
+ * @instr: source address of the original instructions in the kernel text as
+ * generated by the compiler.
+ *
+ * @buf: temporary buffer on which the patching operates. This buffer is
+ * eventually text-poked into the kernel image.
+ *
+ * @replacement/@repl: pointer to the opcodes which are replacing @instr, located
+ * in the .altinstr_replacement section.
+ */
+
+/*
* Fill the buffer with a single effective instruction of size @len.
*
* In order not to issue an ORC stack depth tracking CFI entry (Call Frame Info)
@@ -133,28 +147,28 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
* each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with INT3 and
* *jump* over instead of executing long and daft NOPs.
*/
-static void add_nop(u8 *instr, unsigned int len)
+static void add_nop(u8 *buf, unsigned int len)
{
- u8 *target = instr + len;
+ u8 *target = buf + len;
if (!len)
return;
if (len <= ASM_NOP_MAX) {
- memcpy(instr, x86_nops[len], len);
+ memcpy(buf, x86_nops[len], len);
return;
}
if (len < 128) {
- __text_gen_insn(instr, JMP8_INSN_OPCODE, instr, target, JMP8_INSN_SIZE);
- instr += JMP8_INSN_SIZE;
+ __text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE);
+ buf += JMP8_INSN_SIZE;
} else {
- __text_gen_insn(instr, JMP32_INSN_OPCODE, instr, target, JMP32_INSN_SIZE);
- instr += JMP32_INSN_SIZE;
+ __text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE);
+ buf += JMP32_INSN_SIZE;
}
- for (;instr < target; instr++)
- *instr = INT3_INSN_OPCODE;
+ for (;buf < target; buf++)
+ *buf = INT3_INSN_OPCODE;
}
extern s32 __retpoline_sites[], __retpoline_sites_end[];
@@ -187,12 +201,12 @@ static bool insn_is_nop(struct insn *insn)
* Find the offset of the first non-NOP instruction starting at @offset
* but no further than @len.
*/
-static int skip_nops(u8 *instr, int offset, int len)
+static int skip_nops(u8 *buf, int offset, int len)
{
struct insn insn;
for (; offset < len; offset += insn.length) {
- if (insn_decode_kernel(&insn, &instr[offset]))
+ if (insn_decode_kernel(&insn, &buf[offset]))
break;
if (!insn_is_nop(&insn))
@@ -203,66 +217,32 @@ static int skip_nops(u8 *instr, int offset, int len)
}
/*
- * Optimize a sequence of NOPs, possibly preceded by an unconditional jump
- * to the end of the NOP sequence into a single NOP.
- */
-static bool
-__optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, int *target)
-{
- int i = *next - insn->length;
-
- switch (insn->opcode.bytes[0]) {
- case JMP8_INSN_OPCODE:
- case JMP32_INSN_OPCODE:
- *prev = i;
- *target = *next + insn->immediate.value;
- return false;
- }
-
- if (insn_is_nop(insn)) {
- int nop = i;
-
- *next = skip_nops(instr, *next, len);
- if (*target && *next == *target)
- nop = *prev;
-
- add_nop(instr + nop, *next - nop);
- DUMP_BYTES(ALT, instr, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
- return true;
- }
-
- *target = 0;
- return false;
-}
-
-/*
* "noinline" to cause control flow change and thus invalidate I$ and
* cause refetch after modification.
*/
-static void __init_or_module noinline optimize_nops(u8 *instr, size_t len)
+static void noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
{
- int prev, target = 0;
-
for (int next, i = 0; i < len; i = next) {
struct insn insn;
- if (insn_decode_kernel(&insn, &instr[i]))
+ if (insn_decode_kernel(&insn, &buf[i]))
return;
next = i + insn.length;
- __optimize_nops(instr, len, &insn, &next, &prev, &target);
- }
-}
+ if (insn_is_nop(&insn)) {
+ int nop = i;
-static void __init_or_module noinline optimize_nops_inplace(u8 *instr, size_t len)
-{
- unsigned long flags;
+ /* Has the NOP already been optimized? */
+ if (i + insn.length == len)
+ return;
- local_irq_save(flags);
- optimize_nops(instr, len);
- sync_core();
- local_irq_restore(flags);
+ next = skip_nops(buf, next, len);
+
+ add_nop(buf + nop, next - nop);
+ DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);
+ }
+ }
}
/*
@@ -335,11 +315,9 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
return (target < src || target > src + src_len);
}
-void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+static void __apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
{
- int prev, target = 0;
-
- for (int next, i = 0; i < len; i = next) {
+ for (int next, i = 0; i < instrlen; i = next) {
struct insn insn;
if (WARN_ON_ONCE(insn_decode_kernel(&insn, &buf[i])))
@@ -347,9 +325,6 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
next = i + insn.length;
- if (__optimize_nops(buf, len, &insn, &next, &prev, &target))
- continue;
-
switch (insn.opcode.bytes[0]) {
case 0x0f:
if (insn.opcode.bytes[1] < 0x80 ||
@@ -361,10 +336,10 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
case JMP8_INSN_OPCODE:
case JMP32_INSN_OPCODE:
case CALL_INSN_OPCODE:
- if (need_reloc(next + insn.immediate.value, src, src_len)) {
+ if (need_reloc(next + insn.immediate.value, repl, repl_len)) {
apply_reloc(insn.immediate.nbytes,
buf + i + insn_offset_immediate(&insn),
- src - dest);
+ repl - instr);
}
/*
@@ -372,7 +347,7 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
*/
if (insn.opcode.bytes[0] == JMP32_INSN_OPCODE) {
s32 imm = insn.immediate.value;
- imm += src - dest;
+ imm += repl - instr;
imm += JMP32_INSN_SIZE - JMP8_INSN_SIZE;
if ((imm >> 31) == (imm >> 7)) {
buf[i+0] = JMP8_INSN_OPCODE;
@@ -385,15 +360,21 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
}
if (insn_rip_relative(&insn)) {
- if (need_reloc(next + insn.displacement.value, src, src_len)) {
+ if (need_reloc(next + insn.displacement.value, repl, repl_len)) {
apply_reloc(insn.displacement.nbytes,
buf + i + insn_offset_displacement(&insn),
- src - dest);
+ repl - instr);
}
}
}
}
+void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
+{
+ __apply_relocation(buf, instr, instrlen, repl, repl_len);
+ optimize_nops(instr, buf, repl_len);
+}
+
/* Low-level backend functions usable from alternative code replacements. */
DEFINE_ASM_FUNC(nop_func, "", .entry.text);
EXPORT_SYMBOL_GPL(nop_func);
@@ -464,9 +445,9 @@ static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
void __init_or_module noinline apply_alternatives(struct alt_instr *start,
struct alt_instr *end)
{
- struct alt_instr *a;
- u8 *instr, *replacement;
u8 insn_buff[MAX_PATCH_LEN];
+ u8 *instr, *replacement;
+ struct alt_instr *a;
DPRINTK(ALT, "alt table %px, -> %px", start, end);
@@ -504,7 +485,9 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
* patch if feature is *NOT* present.
*/
if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
- optimize_nops_inplace(instr, a->instrlen);
+ memcpy(insn_buff, instr, a->instrlen);
+ optimize_nops(instr, insn_buff, a->instrlen);
+ text_poke_early(instr, insn_buff, a->instrlen);
continue;
}
@@ -526,7 +509,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
insn_buff[insn_buff_sz] = 0x90;
- apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacementlen);
+ apply_relocation(insn_buff, instr, a->instrlen, replacement, a->replacementlen);
DUMP_BYTES(ALT, instr, a->instrlen, "%px: old_insn: ", instr);
DUMP_BYTES(ALT, replacement, a->replacementlen, "%px: rpl_insn: ", replacement);
@@ -761,7 +744,7 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
len = patch_retpoline(addr, &insn, bytes);
if (len == insn.length) {
- optimize_nops(bytes, len);
+ optimize_nops(addr, bytes, len);
DUMP_BYTES(RETPOLINE, ((u8*)addr), len, "%px: orig: ", addr);
DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr);
text_poke_early(addr, bytes, len);
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index e92ff0c11db8..465647456753 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -185,8 +185,7 @@ static void *patch_dest(void *dest, bool direct)
u8 *pad = dest - tsize;
memcpy(insn_buff, skl_call_thunk_template, tsize);
- apply_relocation(insn_buff, tsize, pad,
- skl_call_thunk_template, tsize);
+ apply_relocation(insn_buff, pad, tsize, skl_call_thunk_template, tsize);
/* Already patched? */
if (!bcmp(pad, insn_buff, tsize))
@@ -308,8 +307,7 @@ static bool is_callthunk(void *addr)
pad = (void *)(dest - tmpl_size);
memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
- apply_relocation(insn_buff, tmpl_size, pad,
- skl_call_thunk_template, tmpl_size);
+ apply_relocation(insn_buff, pad, tmpl_size, skl_call_thunk_template, tmpl_size);
return !bcmp(pad, insn_buff, tmpl_size);
}
@@ -327,8 +325,7 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip)
return 0;
memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
- apply_relocation(insn_buff, tmpl_size, ip,
- skl_call_thunk_template, tmpl_size);
+ apply_relocation(insn_buff, ip, tmpl_size, skl_call_thunk_template, tmpl_size);
memcpy(*pprog, insn_buff, tmpl_size);
*pprog += tmpl_size;
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 946813d816bf..b7d9f530ae16 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -114,6 +114,9 @@ static void do_clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)
if (WARN_ON(feature >= MAX_FEATURE_BITS))
return;
+ if (boot_cpu_has(feature))
+ WARN_ON(alternatives_patched);
+
clear_feature(c, feature);
/* Collect all features to disable, handling dependencies */