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[92.22.57.86]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8a6bbesm9616571f8f.12.2025.10.03.15.53.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Oct 2025 15:53:53 -0700 (PDT) X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d68d6d9a-a0ab-11f0-9809-7dc792cee155 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1759532034; x=1760136834; darn=lists.xenproject.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=L9xT2e+qZfb6j1FUuBgKvZ3n+Jc6Wgtnci0H5fcXpnk=; b=d/u7IctkIlWXySaM6mwf/iYi+EEgyZkPLYWtp9ecOxhcF9SE8CwZEAI37XHioYa35G s38fY0Oz2H6jxXpN6B7nOL3LVFB41HrKBPbe0NdAoHT79dH4JhVEyVJWBUmlBrrDsSon Vd28zFpoMfANKhLs/kaiW13eyDYQtaSHlgsfE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759532034; x=1760136834; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=L9xT2e+qZfb6j1FUuBgKvZ3n+Jc6Wgtnci0H5fcXpnk=; b=CMRgFCjCNr2G/fw8NWO1FyoVP9Jk8aIMLNCSpUwqLmTivXeIrQZ7vA45pzSM4Fdra1 zYbwqRAA6ibBcuUdFxqvoAQlssb+fBW81ALPofwW47UbnoM0YNftQ6WzxsEXGUFr+hac akH5bUZrUA9w18VlPaas/pSgqLGi5opCYuhWhG5e/1IyNVuTl3jcl2fbyAyIWodABq2v kmZFlnlJLK4u9BeBx3c8L4uU1EOg4FEJFdqvasFpLDDgKeot/xNkcg8MdghOGWN9b4qa EVCtXipmUaSQ9uJ5e/lT263EQoFkyOeNkAgVQE6A58kWbU/ZhhX9xK8rLJbf9H7ptEvY 2/oA== X-Gm-Message-State: AOJu0YwnX28bZfLRXlaM89WYDHlqWjtMrx8W1aH/g0ojuC9a5f7UTsh5 YKZWWC3GU8RcEQD9P46yNxIKTQMemuRdVxUDdYWMcxRpWZY3+c0bDkDCbxspYVeMdJhwrOWZG7n p02k9IhfUjw== X-Gm-Gg: ASbGncs0eJzgktQeAEOAWfzLXJA9uo7ngTXie9tU1SnHw3X/HfdI2C3Og+PvfGfOmWG +/RpwJUw33mXuWsytRbHDsfrZlJyG9FQ4cbEiMX7uyQNdPsbBgX6gHO2fdeRR1cG9SaikVBLHq6 fbzs49TGrAS0hREexnEooC8YKr/BvVmIc07sWJgf7vSuuzZG+v9Ye3aB4Y6FQ2lSO/2TiX+Stzf ADBTaeYWGaQBdNJwPbRufLnoBAFAkK0Wrp2QM1YdHXMAwYhBdCvPbVhTDTcFD8xD2gDRahe2iE4 WXWGvg+kf+6sgc2SNymRdCgDUCD4eus4fg1Dz6dNZP+OQjYmcZLkt2zAZ0aCDiVykaImXG+uwwO lysyG9aAX6fFZGxLTRNUHoA7oPRWKY1sj+b0vAcoP68WtS9Q4Ps5aov/sIjvptynbdG5HzubrLp 5SwewwCxNoGThoAdnaHChA X-Google-Smtp-Source: AGHT+IGi4Mtp7sUIenwEW+G9jtr4Ezc1L39uJjX80DcyCAfWrdG2uCI/4ZVImOc792lTjwRvYtIy5g== X-Received: by 2002:a05:6000:3113:b0:3ec:2ef7:2134 with SMTP id ffacd0b85a97d-4256714bb4dmr2598203f8f.18.1759532034126; Fri, 03 Oct 2025 15:53:54 -0700 (PDT) From: Andrew Cooper To: Xen-devel Cc: Andrew Cooper , Jan Beulich , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Subject: [PATCH v3 11/22] x86/fsgsbase: Make gskern accesses safe under FRED Date: Fri, 3 Oct 2025 23:53:23 +0100 Message-Id: <20251003225334.2123667-12-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20251003225334.2123667-1-andrew.cooper3@citrix.com> References: <20251003225334.2123667-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1759532058659116600 Under FRED, the SWAPGS instructions is disallowed. Therefore we must use t= he MSR path instead. read_registers() is in the show_registers() path, so this allows Xen to ren= der it's current state without suffering #UD (and recursing until the stack gua= rd page is hit). All hardware with FRED is expected to have some kind of non-serialising acc= ess to these registers. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 v2: * Broken out of subsequent patch. Rebased over MSR cleanup. --- xen/arch/x86/include/asm/fsgsbase.h | 8 ++++++-- xen/arch/x86/traps.c | 2 +- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/include/asm/fsgsbase.h b/xen/arch/x86/include/asm= /fsgsbase.h index 24862a6bfea7..5faa3a324332 100644 --- a/xen/arch/x86/include/asm/fsgsbase.h +++ b/xen/arch/x86/include/asm/fsgsbase.h @@ -79,7 +79,9 @@ static inline unsigned long read_gs_base(void) =20 static inline unsigned long read_gs_shadow(void) { - if ( read_cr4() & X86_CR4_FSGSBASE ) + unsigned long cr4 =3D read_cr4(); + + if ( !(cr4 & X86_CR4_FRED) && (cr4 & X86_CR4_FSGSBASE) ) return __rdgs_shadow(); else return rdmsr(MSR_SHADOW_GS_BASE); @@ -103,7 +105,9 @@ static inline void write_gs_base(unsigned long base) =20 static inline void write_gs_shadow(unsigned long base) { - if ( read_cr4() & X86_CR4_FSGSBASE ) + unsigned long cr4 =3D read_cr4(); + + if ( !(cr4 & X86_CR4_FRED) && (cr4 & X86_CR4_FSGSBASE) ) __wrgs_shadow(base); else wrmsrns(MSR_SHADOW_GS_BASE, base); diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index d42973660db0..2e3efe45edf4 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -118,7 +118,7 @@ static void read_registers(struct extra_state *state) state->cr3 =3D read_cr3(); state->cr4 =3D read_cr4(); =20 - if ( state->cr4 & X86_CR4_FSGSBASE ) + if ( !(state->cr4 & X86_CR4_FRED) && (state->cr4 & X86_CR4_FSGSBASE) ) { state->fsb =3D __rdfsbase(); state->gsb =3D __rdgsbase(); --=20 2.39.5