From nobody Tue Dec 23 20:07:34 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84A4256772; Wed, 31 Jan 2024 07:21:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706685676; cv=none; b=AT+XKPHV1XV6EGdkyYFxAw3N9pH1JcRtnZK+dSXzBD1g4Gqn+197ejjJbeFapOVhYupjQveTwA/VqRW74OJsxtV1IFljj4PKiOobNNRRE+7HOcD+mmdYIitAoTWlgCAQm+4nTOJBQ5ihynBUqZ9+AXdQNpQ8+ZKKCp835DuotN0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706685676; c=relaxed/simple; bh=06vC6dSb30cXRlyBgUWBCtQ03xSF5Xuzl68Nv5CXQ6g=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=kMCQKtXpB4n+eFgbZG1BgE+cjcuC8/7y/d4J9AxlplG6AbHkio+rc6TvPVh3n2dB8kKOPIahWXqLSCRbEHvqKRn2GMW5gITq00F6qb23pQjwZNxnmrTXw16cHh1kACaIffUCTpqTyg0YsoFIGu8Ho6Wa5xlzKm2uG1wm6iHQDSg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=P1Tsklgy; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=kE/OoDpj; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="P1Tsklgy"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="kE/OoDpj" Date: Wed, 31 Jan 2024 07:21:10 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1706685671; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7EDvqY+FrfhoNiGl/jodCXdh7PZYstJCOtSPDE8BJY4=; b=P1TsklgyQKGqThd716MJsdhpEm++viAFL1y15QrueGf8rjUkDa2GFLq1gqaOP0oI1yl9CO 3a2HnfZ5rKARn5Gy+1awxp2fsSCFaXlVytU7SE4l1i7A6MovbXjHuVXLjem/6LdvNJVHom 22jOj8Tm9J9+DUVSctMI+HZsAqV7eHVEIiTU3F9VXPXbF05hZD7FI3P2ByVDPzDaCWIuf4 dRehA2DEllmaHP6qsn0KsMONeux8R0aG4bitJx1kzZfj3aCAh1cLSh2nDC2AyrG535sa2V oD4tE6mCKVz8T9fVR/CXHx7Hzm8APpwMw+3X4A5uVZ+vCFKeEh2KbTvK34ujyA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1706685671; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7EDvqY+FrfhoNiGl/jodCXdh7PZYstJCOtSPDE8BJY4=; b=kE/OoDpjS/MuE5+LntMenTExv2hPDYNfDa2rKi4fYKOh/g0gW3hyJZtrVywkFYq3Ynw0Ta OGXfGO0sKndKUPAA== From: "tip-bot2 for Xin Li" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/fred] x86/fred: Fixup fault on ERETU by jumping to fred_entrypoint_user Cc: "H. Peter Anvin (Intel)" , Xin Li , Thomas Gleixner , Shan Kang , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20231205105030.8698-30-xin3.li@intel.com> References: <20231205105030.8698-30-xin3.li@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <170668567087.398.14483021835383611163.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the x86/fred branch of tip: Commit-ID: ed63bc7d4953bd5fe93a5c3acef7f485fb216208 Gitweb: https://git.kernel.org/tip/ed63bc7d4953bd5fe93a5c3acef7f485f= b216208 Author: Xin Li AuthorDate: Tue, 05 Dec 2023 02:50:18 -08:00 Committer: Borislav Petkov (AMD) CommitterDate: Tue, 30 Jan 2024 18:20:36 +01:00 x86/fred: Fixup fault on ERETU by jumping to fred_entrypoint_user If the stack frame contains an invalid user context (e.g. due to invalid SS, a non-canonical RIP, etc.) the ERETU instruction will trap (#SS or #GP). >From a Linux point of view, this really should be considered a user space failure, so use the standard fault fixup mechanism to intercept the fault, fix up the exception frame, and redirect execution to fred_entrypoint_user. The end result is that it appears just as if the hardware had taken the exception immediately after completing the transition to user space. Suggested-by: H. Peter Anvin (Intel) Signed-off-by: Xin Li Signed-off-by: Thomas Gleixner Tested-by: Shan Kang Link: https://lore.kernel.org/r/20231205105030.8698-30-xin3.li@intel.com --- arch/x86/entry/entry_64_fred.S | 5 +- arch/x86/include/asm/extable_fixup_types.h | 4 +- arch/x86/mm/extable.c | 78 +++++++++++++++++++++- 3 files changed, 85 insertions(+), 2 deletions(-) diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S index 2271a1c..7fe2722 100644 --- a/arch/x86/entry/entry_64_fred.S +++ b/arch/x86/entry/entry_64_fred.S @@ -3,6 +3,7 @@ * The actual FRED entry points. */ =20 +#include #include =20 #include "calling.h" @@ -34,7 +35,9 @@ SYM_CODE_START_NOALIGN(asm_fred_entrypoint_user) call fred_entry_from_user SYM_INNER_LABEL(asm_fred_exit_user, SYM_L_GLOBAL) FRED_EXIT - ERETU +1: ERETU + + _ASM_EXTABLE_TYPE(1b, asm_fred_entrypoint_user, EX_TYPE_ERETU) SYM_CODE_END(asm_fred_entrypoint_user) =20 /* diff --git a/arch/x86/include/asm/extable_fixup_types.h b/arch/x86/include/= asm/extable_fixup_types.h index fe63120..7acf038 100644 --- a/arch/x86/include/asm/extable_fixup_types.h +++ b/arch/x86/include/asm/extable_fixup_types.h @@ -64,6 +64,8 @@ #define EX_TYPE_UCOPY_LEN4 (EX_TYPE_UCOPY_LEN | EX_DATA_IMM(4)) #define EX_TYPE_UCOPY_LEN8 (EX_TYPE_UCOPY_LEN | EX_DATA_IMM(8)) =20 -#define EX_TYPE_ZEROPAD 20 /* longword load with zeropad on fault */ +#define EX_TYPE_ZEROPAD 20 /* longword load with zeropad on fault */ + +#define EX_TYPE_ERETU 21 =20 #endif diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index 271dcb2..b522933 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -6,6 +6,7 @@ #include =20 #include +#include #include #include #include @@ -223,6 +224,79 @@ static bool ex_handler_ucopy_len(const struct exceptio= n_table_entry *fixup, return ex_handler_uaccess(fixup, regs, trapnr, fault_address); } =20 +#ifdef CONFIG_X86_FRED +static bool ex_handler_eretu(const struct exception_table_entry *fixup, + struct pt_regs *regs, unsigned long error_code) +{ + struct pt_regs *uregs =3D (struct pt_regs *)(regs->sp - offsetof(struct p= t_regs, orig_ax)); + unsigned short ss =3D uregs->ss; + unsigned short cs =3D uregs->cs; + + /* + * Move the NMI bit from the invalid stack frame, which caused ERETU + * to fault, to the fault handler's stack frame, thus to unblock NMI + * with the fault handler's ERETS instruction ASAP if NMI is blocked. + */ + regs->fred_ss.nmi =3D uregs->fred_ss.nmi; + + /* + * Sync event information to uregs, i.e., the ERETU return frame, but + * is it safe to write to the ERETU return frame which is just above + * current event stack frame? + * + * The RSP used by FRED to push a stack frame is not the value in %rsp, + * it is calculated from %rsp with the following 2 steps: + * 1) RSP =3D %rsp - (IA32_FRED_CONFIG & 0x1c0) // Reserve N*64 bytes + * 2) RSP =3D RSP & ~0x3f // Align to a 64-byte cache line + * when an event delivery doesn't trigger a stack level change. + * + * Here is an example with N*64 (N=3D1) bytes reserved: + * + * 64-byte cache line =3D=3D> ______________ + * |___Reserved___| + * |__Event_data__| + * |_____SS_______| + * |_____RSP______| + * |_____FLAGS____| + * |_____CS_______| + * |_____IP_______| + * 64-byte cache line =3D=3D> |__Error_code__| <=3D=3D ERETU return frame + * |______________| + * |______________| + * |______________| + * |______________| + * |______________| + * |______________| + * |______________| + * 64-byte cache line =3D=3D> |______________| <=3D=3D RSP after step 1)= and 2) + * |___Reserved___| + * |__Event_data__| + * |_____SS_______| + * |_____RSP______| + * |_____FLAGS____| + * |_____CS_______| + * |_____IP_______| + * 64-byte cache line =3D=3D> |__Error_code__| <=3D=3D ERETS return frame + * + * Thus a new FRED stack frame will always be pushed below a previous + * FRED stack frame ((N*64) bytes may be reserved between), and it is + * safe to write to a previous FRED stack frame as they never overlap. + */ + fred_info(uregs)->edata =3D fred_event_data(regs); + uregs->ssx =3D regs->ssx; + uregs->fred_ss.ss =3D ss; + /* The NMI bit was moved away above */ + uregs->fred_ss.nmi =3D 0; + uregs->csx =3D regs->csx; + uregs->fred_cs.sl =3D 0; + uregs->fred_cs.wfe =3D 0; + uregs->cs =3D cs; + uregs->orig_ax =3D error_code; + + return ex_handler_default(fixup, regs); +} +#endif + int ex_get_fixup_type(unsigned long ip) { const struct exception_table_entry *e =3D search_exception_tables(ip); @@ -300,6 +374,10 @@ int fixup_exception(struct pt_regs *regs, int trapnr, = unsigned long error_code, return ex_handler_ucopy_len(e, regs, trapnr, fault_addr, reg, imm); case EX_TYPE_ZEROPAD: return ex_handler_zeropad(e, regs, fault_addr); +#ifdef CONFIG_X86_FRED + case EX_TYPE_ERETU: + return ex_handler_eretu(e, regs, error_code); +#endif } BUG(); }