[PATCH] x86/ptrace: Fix xfpregs_set()'s incorrect xmm clearing

[Borislav Petkov <bp@alien8.de>]

Lemme send it out as Luto looks busy.

If there are no complaints I'll queue it in a couple of days...

Thx.

---
From: Andy Lutomirski <luto@kernel.org>
Date: Mon, 31 Jan 2022 12:38:47 -0800
Subject: [PATCH] x86/ptrace: Fix xfpregs_set()'s incorrect xmm clearing
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xfpregs_set() handles 32-bit REGSET_XFP and 64-bit REGSET_FP. The actual
code treats these regsets as modern FX state (i.e. the beginning part of
XSTATE). The declarations of the regsets thought they were the legacy
i387 format. The code thought they were the 32-bit (no xmm8..15) variant
of XSTATE and, for good measure, made the high bits disappear by zeroing
the wrong part of the buffer. The latter broke ptrace, and everything
else confused anyone trying to understand the code. In particular, the
nonsense definitions of the regsets confused me when I wrote this code.

Clean this all up. Change the declarations to match reality (which
shouldn't change the generated code, let alone the ABI) and fix
xfpregs_set() to clear the correct bits and to only do so for 32-bit
callers.

Fixes: 6164331d15f7 ("x86/fpu: Rewrite xfpregs_set()")
Reported-by: Luís Ferreira <contact@lsferreira.net>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215524
---
 arch/x86/kernel/fpu/regset.c | 9 ++++-----
 arch/x86/kernel/ptrace.c     | 4 ++--
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 437d7c930c0b..75ffaef8c299 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -91,11 +91,9 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 		const void *kbuf, const void __user *ubuf)
 {
 	struct fpu *fpu = &target->thread.fpu;
-	struct user32_fxsr_struct newstate;
+	struct fxregs_state newstate;
 	int ret;
 
-	BUILD_BUG_ON(sizeof(newstate) != sizeof(struct fxregs_state));
-
 	if (!cpu_feature_enabled(X86_FEATURE_FXSR))
 		return -ENODEV;
 
@@ -116,9 +114,10 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 	/* Copy the state  */
 	memcpy(&fpu->fpstate->regs.fxsave, &newstate, sizeof(newstate));
 
-	/* Clear xmm8..15 */
+	/* Clear xmm8..15 for 32-bit callers */
 	BUILD_BUG_ON(sizeof(fpu->__fpstate.regs.fxsave.xmm_space) != 16 * 16);
-	memset(&fpu->fpstate->regs.fxsave.xmm_space[8], 0, 8 * 16);
+	if (in_ia32_syscall())
+		memset(&fpu->fpstate->regs.fxsave.xmm_space[8*4], 0, 8 * 16);
 
 	/* Mark FP and SSE as in use when XSAVE is enabled */
 	if (use_xsave())
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 6d2244c94799..8d2f2f995539 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1224,7 +1224,7 @@ static struct user_regset x86_64_regsets[] __ro_after_init = {
 	},
 	[REGSET_FP] = {
 		.core_note_type = NT_PRFPREG,
-		.n = sizeof(struct user_i387_struct) / sizeof(long),
+		.n = sizeof(struct fxregs_state) / sizeof(long),
 		.size = sizeof(long), .align = sizeof(long),
 		.active = regset_xregset_fpregs_active, .regset_get = xfpregs_get, .set = xfpregs_set
 	},
@@ -1271,7 +1271,7 @@ static struct user_regset x86_32_regsets[] __ro_after_init = {
 	},
 	[REGSET_XFP] = {
 		.core_note_type = NT_PRXFPREG,
-		.n = sizeof(struct user32_fxsr_struct) / sizeof(u32),
+		.n = sizeof(struct fxregs_state) / sizeof(u32),
 		.size = sizeof(u32), .align = sizeof(u32),
 		.active = regset_xregset_fpregs_active, .regset_get = xfpregs_get, .set = xfpregs_set
 	},
-- 
2.29.2

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette