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x86/insn: Stop decoding i64 instructions in x86-64 mode at opcode

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In commit 2e044911be ("x86/traps: Decode 0xEA instructions as #UD")
FineIBT starts using 0xEA as an invalid instruction like UD2. But
insn decoder always returns the length of "0xea" instruction as 7
because it does not check the (i64) superscript.

The x86 instruction decoder should also decode 0xEA on x86-64 as
a one-byte invalid instruction by decoding the "(i64)" superscript tag.

This stops decoding instruction which has (i64) but does not have (o64)
superscript in 64-bit mode at opcode and skips other fields.

With this change, insn_decoder_test says 0xea is 1 byte length if
x86-64 (-y option means 64-bit):

   $ printf "0:\tea\t\n" | insn_decoder_test -y -v
   insn_decoder_test: success: Decoded and checked 1 instructions

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/174580490000.388420.5225447607417115496.stgit@devnote2
This commit is contained in:
Masami Hiramatsu (Google) 2025-04-28 10:48:20 +09:00 committed by Ingo Molnar
parent ca698ec2f0
commit 4b626015e1
8 changed files with 44 additions and 8 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
arch/x86/include/asm/inat.h
View file

@ -82,6 +82,7 @@
#define INAT_NO_REX2 (1 << (INAT_FLAG_OFFS + 8))
#define INAT_REX2_VARIANT (1 << (INAT_FLAG_OFFS + 9))
#define INAT_EVEX_SCALABLE (1 << (INAT_FLAG_OFFS + 10))
#define INAT_INV64 (1 << (INAT_FLAG_OFFS + 11))
/* Attribute making macros for attribute tables */
#define INAT_MAKE_PREFIX(pfx) (pfx << INAT_PFX_OFFS)
#define INAT_MAKE_ESCAPE(esc) (esc << INAT_ESC_OFFS)
@ -242,4 +243,9 @@ static inline int inat_evex_scalable(insn_attr_t attr)
{
return attr & INAT_EVEX_SCALABLE;
}
static inline int inat_is_invalid64(insn_attr_t attr)
{
return attr & INAT_INV64;
}
#endif

7
arch/x86/lib/insn.c
View file

@ -324,6 +324,11 @@ int insn_get_opcode(struct insn *insn)
}
insn->attr = inat_get_opcode_attribute(op);
if (insn->x86_64 && inat_is_invalid64(insn->attr)) {
/* This instruction is invalid, like UD2. Stop decoding. */
insn->attr &= INAT_INV64;
}
while (inat_is_escape(insn->attr)) {
/* Get escaped opcode */
op = get_next(insn_byte_t, insn);
@ -337,6 +342,7 @@ int insn_get_opcode(struct insn *insn)
insn->attr = 0;
return -EINVAL;
}
end:
opcode->got = 1;
return 0;
@ -658,7 +664,6 @@ int insn_get_immediate(struct insn *insn)
}
if (!inat_has_immediate(insn->attr))
/* no immediates */
goto done;
switch (inat_immediate_size(insn->attr)) {

6
arch/x86/lib/x86-opcode-map.txt
View file

@ -147,7 +147,7 @@ AVXcode:
# 0x60 - 0x6f
60: PUSHA/PUSHAD (i64)
61: POPA/POPAD (i64)
62: BOUND Gv,Ma (i64) | EVEX (Prefix)
62: BOUND Gv,Ma (i64) | EVEX (Prefix),(o64)
63: ARPL Ew,Gw (i64) | MOVSXD Gv,Ev (o64)
64: SEG=FS (Prefix)
65: SEG=GS (Prefix)
@ -253,8 +253,8 @@ c0: Grp2 Eb,Ib (1A)
c1: Grp2 Ev,Ib (1A)
c2: RETN Iw (f64)
c3: RETN
c4: LES Gz,Mp (i64) | VEX+2byte (Prefix)
c5: LDS Gz,Mp (i64) | VEX+1byte (Prefix)
c4: LES Gz,Mp (i64) | VEX+2byte (Prefix),(o64)
c5: LDS Gz,Mp (i64) | VEX+1byte (Prefix),(o64)
c6: Grp11A Eb,Ib (1A)
c7: Grp11B Ev,Iz (1A)
c8: ENTER Iw,Ib

7
arch/x86/tools/gen-insn-attr-x86.awk
View file

@ -64,6 +64,8 @@ BEGIN {
modrm_expr = "^([CDEGMNPQRSUVW/][a-z]+|NTA|T[012])"
force64_expr = "\\([df]64\\)"
invalid64_expr = "\\(i64\\)"
only64_expr = "\\(o64\\)"
rex_expr = "^((REX(\\.[XRWB]+)+)|(REX$))"
rex2_expr = "\\(REX2\\)"
no_rex2_expr = "\\(!REX2\\)"
@ -319,6 +321,11 @@ function convert_operands(count,opnd, i,j,imm,mod)
if (match(ext, force64_expr))
flags = add_flags(flags, "INAT_FORCE64")
# check invalid in 64-bit (and no only64)
if (match(ext, invalid64_expr) &&
!match($0, only64_expr))
flags = add_flags(flags, "INAT_INV64")
# check REX2 not allowed
if (match(ext, no_rex2_expr))
flags = add_flags(flags, "INAT_NO_REX2")

6
tools/arch/x86/include/asm/inat.h
View file

@ -82,6 +82,7 @@
#define INAT_NO_REX2 (1 << (INAT_FLAG_OFFS + 8))
#define INAT_REX2_VARIANT (1 << (INAT_FLAG_OFFS + 9))
#define INAT_EVEX_SCALABLE (1 << (INAT_FLAG_OFFS + 10))
#define INAT_INV64 (1 << (INAT_FLAG_OFFS + 11))
/* Attribute making macros for attribute tables */
#define INAT_MAKE_PREFIX(pfx) (pfx << INAT_PFX_OFFS)
#define INAT_MAKE_ESCAPE(esc) (esc << INAT_ESC_OFFS)
@ -242,4 +243,9 @@ static inline int inat_evex_scalable(insn_attr_t attr)
{
return attr & INAT_EVEX_SCALABLE;
}
static inline int inat_is_invalid64(insn_attr_t attr)
{
return attr & INAT_INV64;
}
#endif

7
tools/arch/x86/lib/insn.c
View file

@ -324,6 +324,11 @@ int insn_get_opcode(struct insn *insn)
}
insn->attr = inat_get_opcode_attribute(op);
if (insn->x86_64 && inat_is_invalid64(insn->attr)) {
/* This instruction is invalid, like UD2. Stop decoding. */
insn->attr &= INAT_INV64;
}
while (inat_is_escape(insn->attr)) {
/* Get escaped opcode */
op = get_next(insn_byte_t, insn);
@ -337,6 +342,7 @@ int insn_get_opcode(struct insn *insn)
insn->attr = 0;
return -EINVAL;
}
end:
opcode->got = 1;
return 0;
@ -658,7 +664,6 @@ int insn_get_immediate(struct insn *insn)
}
if (!inat_has_immediate(insn->attr))
/* no immediates */
goto done;
switch (inat_immediate_size(insn->attr)) {

6
tools/arch/x86/lib/x86-opcode-map.txt
View file

@ -147,7 +147,7 @@ AVXcode:
# 0x60 - 0x6f
60: PUSHA/PUSHAD (i64)
61: POPA/POPAD (i64)
62: BOUND Gv,Ma (i64) | EVEX (Prefix)
62: BOUND Gv,Ma (i64) | EVEX (Prefix),(o64)
63: ARPL Ew,Gw (i64) | MOVSXD Gv,Ev (o64)
64: SEG=FS (Prefix)
65: SEG=GS (Prefix)
@ -253,8 +253,8 @@ c0: Grp2 Eb,Ib (1A)
c1: Grp2 Ev,Ib (1A)
c2: RETN Iw (f64)
c3: RETN
c4: LES Gz,Mp (i64) | VEX+2byte (Prefix)
c5: LDS Gz,Mp (i64) | VEX+1byte (Prefix)
c4: LES Gz,Mp (i64) | VEX+2byte (Prefix),(o64)
c5: LDS Gz,Mp (i64) | VEX+1byte (Prefix),(o64)
c6: Grp11A Eb,Ib (1A)
c7: Grp11B Ev,Iz (1A)
c8: ENTER Iw,Ib

7
tools/arch/x86/tools/gen-insn-attr-x86.awk
View file

@ -64,6 +64,8 @@ BEGIN {
modrm_expr = "^([CDEGMNPQRSUVW/][a-z]+|NTA|T[012])"
force64_expr = "\\([df]64\\)"
invalid64_expr = "\\(i64\\)"
only64_expr = "\\(o64\\)"
rex_expr = "^((REX(\\.[XRWB]+)+)|(REX$))"
rex2_expr = "\\(REX2\\)"
no_rex2_expr = "\\(!REX2\\)"
@ -319,6 +321,11 @@ function convert_operands(count,opnd, i,j,imm,mod)
if (match(ext, force64_expr))
flags = add_flags(flags, "INAT_FORCE64")
# check invalid in 64-bit (and no only64)
if (match(ext, invalid64_expr) &&
!match($0, only64_expr))
flags = add_flags(flags, "INAT_INV64")
# check REX2 not allowed
if (match(ext, no_rex2_expr))
flags = add_flags(flags, "INAT_NO_REX2")