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x86/tdx: Fix zero-extension for 32-bit port I/O

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According to x86 architecture rules, 32-bit operations zero-extend the
result to 64 bits. The current implementation of handle_in() only masks
the lower 32 bits, which preserves the upper 32 bits of RAX when a
32-bit port IN instruction is emulated.

Use insn_assign_reg() to write the result back into RAX with proper
partial-register-write semantics: 1- and 2-byte forms leave the upper
bits untouched, the 4-byte form zero-extends to the full register.

Fixes: 0314994883 ("x86/tdx: Port I/O: Add runtime hypercalls")
Reported-by: Borys Tsyrulnikov <tsyrulnikov.borys@gmail.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/all/CAKw_Dz96rfSQc6Rn+9QBcUFHhmkK+9zu+P=bxowfZwxrATCBRg@mail.gmail.com/
Cc:stable@vger.kernel.org
Link: https://patch.msgid.link/20260713133753.223947-4-kirill@shutemov.name
This commit is contained in:
Kiryl Shutsemau (Meta) 2026-07-13 14:37:53 +01:00 committed by Dave Hansen
parent 1fe104b048
commit 941370fc93
1 changed files with 3 additions and 5 deletions
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8
arch/x86/coco/tdx/tdx.c
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@ -694,8 +694,8 @@ static bool handle_in(struct pt_regs *regs, int size, int port)
.r13 = PORT_READ,
.r14 = port,
};
u64 mask = GENMASK(BITS_PER_BYTE * size - 1, 0);
bool success;
u64 val;
/*
* Emulate the I/O read via hypercall. More info about ABI can be found
@ -703,11 +703,9 @@ static bool handle_in(struct pt_regs *regs, int size, int port)
* "TDG.VP.VMCALL<Instruction.IO>".
*/
success = !__tdx_hypercall(&args);
val = success ? args.r11 : 0;
/* Update part of the register affected by the emulated instruction */
regs->ax &= ~mask;
if (success)
regs->ax |= args.r11 & mask;
insn_assign_reg(&regs->ax, val, size);
return success;
}