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[37.24.206.209]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5dcd8dcaf17sm1634658a12.15.2025.02.05.02.30.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Feb 2025 02:30:23 -0800 (PST) Message-ID: Date: Wed, 5 Feb 2025 11:30:22 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/xen: fix xen_hypercall_hvm() to not clobber %rbx To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Cc: Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , xen-devel@lists.xenproject.org, Andrew Cooper , linux-kernel@vger.kernel.org, x86@kernel.org References: <20250205091056.17796-1-jgross@suse.com> <121c5edb-9268-4258-9735-38e4e0f226ad@citrix.com> <3bb7aa63-9acd-4142-b7d6-bde3e92325ef@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 05.02.2025 11:04, Jürgen Groß wrote: > On 05.02.25 10:38, Andrew Cooper wrote: >> On 05/02/2025 9:17 am, Jürgen Groß wrote: >>> On 05.02.25 10:16, Andrew Cooper wrote: >>>> On 05/02/2025 9:10 am, Juergen Gross wrote: >>>>> xen_hypercall_hvm(), which is used when running as a Xen PVH guest at >>>>> most only once during early boot, is clobbering %rbx. Depending on >>>>> whether the caller relies on %rbx to be preserved across the call or >>>>> not, this clobbering might result in an early crash of the system. >>>>> >>>>> This can be avoided by not modifying %rbx in xen_hypercall_hvm(). >>>>> >>>>> Fixes: b4845bb63838 ("x86/xen: add central hypercall functions") >>>>> Signed-off-by: Juergen Gross >>>>> --- >>>>>   arch/x86/xen/xen-head.S | 3 +-- >>>>>   1 file changed, 1 insertion(+), 2 deletions(-) >>>>> >>>>> diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S >>>>> index 9252652afe59..4378b817ed32 100644 >>>>> --- a/arch/x86/xen/xen-head.S >>>>> +++ b/arch/x86/xen/xen-head.S >>>>> @@ -117,8 +117,7 @@ SYM_FUNC_START(xen_hypercall_hvm) >>>> >>>> The 32bit case, out of context up here, also clobbers %ebx. >>>> >>>> ~Andrew >>>> >>>>>       pop %ebx >>> >>> It does not, as this part of the context is showing. >> >> Hmm, so it is, and worse, it can't be changed to match the 64bit side. >> That's nasty. >> >> But while I'm here looking at the code, what's up with >> >> #ifdef CONFIG_FRAME_POINTER >>         pushq $0        /* Dummy push for stack alignment. */ >> #endif >> >> ? >> >> That's covered by FRAME_{START,END} normally, and Linux's preferred >> stack alignment is 8 not 16. > > I've added this due to a review comment by Jan. As he is more into ABI > matters, I believed him. > > Google is telling me you are right, so I'll remove those extra hunks in > V2 of the patch adding FRAME_END. Oh, I'm sorry for misleading you. Clearly I must have been mis-remembering (or things may have changed, and I should have re-checked). Jan