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Subject[tip: x86/seves] x86/umip: Factor out instruction decoding
The following commit has been merged into the x86/seves branch of tip:

Commit-ID: 172639d79977ca7b5ce6f84f6606262f4081718f
Gitweb: https://git.kernel.org/tip/172639d79977ca7b5ce6f84f6606262f4081718f
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 07 Sep 2020 15:15:10 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 07 Sep 2020 19:45:24 +02:00

x86/umip: Factor out instruction decoding

Factor out the code used to decode an instruction with the correct
address and operand sizes to a helper function.

No functional changes.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-10-joro@8bytes.org
---
arch/x86/include/asm/insn-eval.h | 2 +-
arch/x86/kernel/umip.c | 23 +----------------
arch/x86/lib/insn-eval.c | 45 +++++++++++++++++++++++++++++++-
3 files changed, 48 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index b8b9ef1..392b4fe 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -21,5 +21,7 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx);
int insn_get_code_seg_params(struct pt_regs *regs);
int insn_fetch_from_user(struct pt_regs *regs,
unsigned char buf[MAX_INSN_SIZE]);
+bool insn_decode(struct insn *insn, struct pt_regs *regs,
+ unsigned char buf[MAX_INSN_SIZE], int buf_size);

#endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index ad135be..f6225bf 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -342,7 +342,6 @@ bool fixup_umip_exception(struct pt_regs *regs)
unsigned long *reg_addr;
void __user *uaddr;
struct insn insn;
- int seg_defs;

if (!regs)
return false;
@@ -357,27 +356,7 @@ bool fixup_umip_exception(struct pt_regs *regs)
if (!nr_copied)
return false;

- insn_init(&insn, buf, nr_copied, user_64bit_mode(regs));
-
- /*
- * Override the default operand and address sizes with what is specified
- * in the code segment descriptor. The instruction decoder only sets
- * the address size it to either 4 or 8 address bytes and does nothing
- * for the operand bytes. This OK for most of the cases, but we could
- * have special cases where, for instance, a 16-bit code segment
- * descriptor is used.
- * If there is an address override prefix, the instruction decoder
- * correctly updates these values, even for 16-bit defaults.
- */
- seg_defs = insn_get_code_seg_params(regs);
- if (seg_defs == -EINVAL)
- return false;
-
- insn.addr_bytes = INSN_CODE_SEG_ADDR_SZ(seg_defs);
- insn.opnd_bytes = INSN_CODE_SEG_OPND_SZ(seg_defs);
-
- insn_get_length(&insn);
- if (nr_copied < insn.length)
+ if (!insn_decode(&insn, regs, buf, nr_copied))
return false;

umip_inst = identify_insn(&insn);
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 947b7f1..2323c85 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1405,3 +1405,48 @@ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])

return MAX_INSN_SIZE - not_copied;
}
+
+/**
+ * insn_decode() - Decode an instruction
+ * @insn: Structure to store decoded instruction
+ * @regs: Structure with register values as seen when entering kernel mode
+ * @buf: Buffer containing the instruction bytes
+ * @buf_size: Number of instruction bytes available in buf
+ *
+ * Decodes the instruction provided in buf and stores the decoding results in
+ * insn. Also determines the correct address and operand sizes.
+ *
+ * Returns:
+ *
+ * True if instruction was decoded, False otherwise.
+ */
+bool insn_decode(struct insn *insn, struct pt_regs *regs,
+ unsigned char buf[MAX_INSN_SIZE], int buf_size)
+{
+ int seg_defs;
+
+ insn_init(insn, buf, buf_size, user_64bit_mode(regs));
+
+ /*
+ * Override the default operand and address sizes with what is specified
+ * in the code segment descriptor. The instruction decoder only sets
+ * the address size it to either 4 or 8 address bytes and does nothing
+ * for the operand bytes. This OK for most of the cases, but we could
+ * have special cases where, for instance, a 16-bit code segment
+ * descriptor is used.
+ * If there is an address override prefix, the instruction decoder
+ * correctly updates these values, even for 16-bit defaults.
+ */
+ seg_defs = insn_get_code_seg_params(regs);
+ if (seg_defs == -EINVAL)
+ return false;
+
+ insn->addr_bytes = INSN_CODE_SEG_ADDR_SZ(seg_defs);
+ insn->opnd_bytes = INSN_CODE_SEG_OPND_SZ(seg_defs);
+
+ insn_get_length(insn);
+ if (buf_size < insn->length)
+ return false;
+
+ return true;
+}
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