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Peter Anvin" Subject: [PATCH] x86/insn-eval: Fix signedness bug in segment selector handling Date: Wed, 1 Apr 2026 12:13:10 +0200 Message-ID: <20260401101326.319649-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" get_segment_selector() returns a short, while callers use the pattern: short sel =3D get_segment_selector(...); if (sel < 0) return -ERR; Segment selectors are 16-bit values, but storing them in a signed 16-bit type means values with the MSB set (>=3D 0x8000) become negative. This causes valid selectors to be misinterpreted as errors by the 'sel < 0' check. Change get_segment_selector() to return int and update all call sites to use 'int sel' to avoid unintended sign extension and keep error handling via negative return values correct. Additionally, remove the explicit & 0xffff masking when reading segment registers. The compiler already zero-extends unsigned 16-bit values when loading them into a wider type, so the masking is redundant. With this change, valid segment selectors are no longer confused with error returns. Signed-off-by: Uros Bizjak Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" --- arch/x86/lib/insn-eval.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index e03eeec55cfe..b8847ce0b282 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -340,18 +340,18 @@ static int resolve_seg_reg(struct insn *insn, struct = pt_regs *regs, int regoff) * * -EINVAL on error. */ -static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx) +static int get_segment_selector(struct pt_regs *regs, int seg_reg_idx) { - unsigned short sel; + unsigned int sel; =20 #ifdef CONFIG_X86_64 switch (seg_reg_idx) { case INAT_SEG_REG_IGNORE: return 0; case INAT_SEG_REG_CS: - return (unsigned short)(regs->cs & 0xffff); + return regs->cs; case INAT_SEG_REG_SS: - return (unsigned short)(regs->ss & 0xffff); + return regs->ss; case INAT_SEG_REG_DS: savesegment(ds, sel); return sel; @@ -373,9 +373,9 @@ static short get_segment_selector(struct pt_regs *regs,= int seg_reg_idx) if (v8086_mode(regs)) { switch (seg_reg_idx) { case INAT_SEG_REG_CS: - return (unsigned short)(regs->cs & 0xffff); + return regs->cs; case INAT_SEG_REG_SS: - return (unsigned short)(regs->ss & 0xffff); + return regs->ss; case INAT_SEG_REG_DS: return vm86regs->ds; case INAT_SEG_REG_ES: @@ -392,15 +392,15 @@ static short get_segment_selector(struct pt_regs *reg= s, int seg_reg_idx) =20 switch (seg_reg_idx) { case INAT_SEG_REG_CS: - return (unsigned short)(regs->cs & 0xffff); + return regs->cs; case INAT_SEG_REG_SS: - return (unsigned short)(regs->ss & 0xffff); + return regs->ss; case INAT_SEG_REG_DS: - return (unsigned short)(regs->ds & 0xffff); + return regs->ds; case INAT_SEG_REG_ES: - return (unsigned short)(regs->es & 0xffff); + return regs->es; case INAT_SEG_REG_FS: - return (unsigned short)(regs->fs & 0xffff); + return regs->fs; case INAT_SEG_REG_GS: savesegment(gs, sel); return sel; @@ -688,7 +688,7 @@ static bool get_desc(struct desc_struct *out, unsigned = short sel) unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx) { struct desc_struct desc; - short sel; + int sel; =20 sel =3D get_segment_selector(regs, seg_reg_idx); if (sel < 0) @@ -756,7 +756,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs= , int seg_reg_idx) { struct desc_struct desc; unsigned long limit; - short sel; + int sel; =20 sel =3D get_segment_selector(regs, seg_reg_idx); if (sel < 0) @@ -803,7 +803,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs= , int seg_reg_idx) int insn_get_code_seg_params(struct pt_regs *regs) { struct desc_struct desc; - short sel; + int sel; =20 if (v8086_mode(regs)) /* Address and operand size are both 16-bit. */ --=20 2.53.0